Hubbry Logo
Routing Information ProtocolRouting Information ProtocolMain
Open search
Routing Information Protocol
Community hub
Routing Information Protocol
logo
7 pages, 0 posts
0 subscribers
Be the first to start a discussion here.
Be the first to start a discussion here.
Routing Information Protocol
Routing Information Protocol
Routing Information Protocol
View on Wikipedia
from Wikipedia
Internet protocol suite
Application layer
Transport layer
Internet layer
Link layer

The Routing Information Protocol (RIP) is one of the oldest distance-vector routing protocols which employs the hop count as a routing metric. RIP prevents routing loops by implementing a limit on the number of hops allowed in a path from source to destination. The largest number of hops allowed for RIP is 15, which limits the size of networks that RIP can support.

RIP implements the split horizon, route poisoning, and holddown mechanisms to prevent incorrect routing information from being propagated.

In RIPv1 routers broadcast updates with their routing table every 30 seconds. In the early deployments, routing tables were small enough that the traffic was not significant. As networks grew in size, however, it became evident there could be a massive traffic burst every 30 seconds, even if the routers had been initialized at random times.

In most networking environments, RIP is not the preferred choice of routing protocol, as its time to converge and scalability are poor compared to EIGRP, OSPF, or IS-IS. However, it is easy to configure, because RIP does not require any parameters, unlike other protocols.

RIP uses the User Datagram Protocol (UDP) as its transport protocol, and is assigned the reserved port number 520.[1]

Development of distance-vector routing

[edit]

Based on the Bellman–Ford algorithm and the Ford–Fulkerson algorithm, distance-vector routing protocols started to be implemented from 1969 onwards in data networks such as the ARPANET and CYCLADES. The predecessor of RIP was the Gateway Information Protocol (GWINFO) which was developed by Xerox in the mid-1970s to route its experimental network. As part of the Xerox Network Systems (XNS) protocol suite GWINFO transformed into the XNS Routing Information Protocol. This XNS RIP in turn became the basis for early routing protocols, such as Novell's IPX RIP, AppleTalk's Routing Table Maintenance Protocol (RTMP), and the IP RIP. The 1982 Berkeley Software Distribution of the UNIX operating system implemented RIP in the routed daemon. The 4.2BSD release proved popular and became the basis for subsequent UNIX versions, which implemented RIP in the routed or gated daemon. Ultimately, RIP had been extensively deployed[2] before the standard, written by Charles Hedrick, was passed as RIPv1 in 1988.[3]

The RIP hop count

[edit]

The routing metric used by RIP counts the number of routers that need to be passed to reach a destination IP network. The hop count 0 denotes a network that is directly connected to the router. 16 hops denote a network that is unreachable, according to the RIP hop limit.[4]

Versions

[edit]

There are three standardized versions of the Routing Information Protocol: RIPv1 and RIPv2 for IPv4, and RIPng for IPv6.

RIP version 1

[edit]

The original specification of RIP was published in 1988.[3] When starting up, and every 30 seconds thereafter, a router with RIPv1 implementation broadcasts to 255.255.255.255 a request message through every RIPv1 enabled interface. Neighbouring routers receiving the request message respond with a RIPv1 segment, containing their routing table. The requesting router updates its own routing table, with the reachable IP network address, hop count and next hop, that is the router interface IP address from which the RIPv1 response was sent. As the requesting router receives updates from different neighbouring routers it will only update the reachable networks in its routing table, if it receives information about a reachable network it has not yet in its routing table or information that a network it has in its routing table is reachable with a lower hop count. Therefore, a RIPv1 router will in most cases only have one entry for a reachable network, the one with the lowest hop count. If a router receives information from two different neighbouring router that the same network is reachable with the same hop count but via two different routes, the network will be entered into the routing table two times with different next hop routers. The RIPv1 enabled router will then perform what is known as equal-cost load balancing for IP packets.[4]

RIPv1 enabled routers not only request the routing tables of other routers every 30 seconds, they also listen to incoming requests from neighbouring routers and send their own routing table in turn. RIPv1 routing tables are therefore updated every 25 to 35 seconds.[4] The RIPv1 protocol adds a small random time variable to the update time, to avoid routing tables synchronizing across a LAN.[5] It was thought, as a result of random initialization, the routing updates would spread out in time, but this was not true in practice. Sally Floyd and Van Jacobson showed in 1994 that, without slight randomization of the update timer, the timers synchronized over time.[6]

RIPv1 can be configured into silent mode, so that a router requests and processes neighbouring routing tables, and keeps its routing table and hop count for reachable networks up to date, but does not needlessly send its own routing table into the network. Silent mode is commonly implemented to hosts.[7]

RIPv1 uses classful routing. The periodic routing updates do not carry subnet information, lacking support for variable length subnet masks (VLSM). This limitation makes it impossible to have different-sized subnets inside of the same network class. In other words, all subnets in a network class must have the same size. There is also no support for router authentication, making RIP vulnerable to various attacks.

RIP version 2

[edit]

Due to the deficiencies of the original RIP specification, RIP version 2 (RIPv2) was developed in 1993,[4] published in 1994,[8] and declared Internet Standard 56 in 1998.[9] It included the ability to carry subnet information, thus supporting Classless Inter-Domain Routing (CIDR). To maintain backward compatibility, the hop count limit of 15 remained. RIPv2 has facilities to fully interoperate with the earlier specification if all Must Be Zero protocol fields in the RIPv1 messages are properly specified. In addition, a compatibility switch feature[9] allows fine-grained interoperability adjustments.

In an effort to avoid unnecessary load on hosts that do not participate in routing, RIPv2 multicasts the entire routing table to all adjacent routers at the address 224.0.0.9, as opposed to RIPv1 which uses broadcast. Unicast addressing is still allowed for special applications.

(MD5) authentication for RIP was introduced in 1997.[10][11]

Route tags were also added in RIP version 2. This functionality allows a distinction between routes learned from the RIP protocol and routes learned from other protocols.

RIPng

[edit]

RIPng (RIP next generation) is an extension of RIPv2 for support of IPv6, the next generation Internet Protocol.[12] The main differences between RIPv2 and RIPng are:

  • Support of IPv6 networking.
  • While RIPv2 supports RIPv1 updates authentication, RIPng does not. IPv6 routers were, at the time, supposed to use IPsec for authentication.[citation needed]
  • RIPv2 encodes the next-hop into each route entry, RIPng requires specific encoding of the next hop for a set of route entries.

RIPng sends updates on UDP port 521 using the multicast group ff02::9.

RIP messages between routers

[edit]

RIP messages use the User Datagram Protocol on port 520 and all RIP messages exchanged between routers are encapsulated in a UDP datagram.[4]

RIPv1 Messages

[edit]

RIP defined two types of messages:

Request Message
Asking a neighbouring RIPv1 enabled router to send its routing table.
Response Message
Carries the routing table of a router.

Timers

[edit]

The routing information protocol uses the following timers as part of its operation:[13]

Update Timer
Controls the interval between two gratuitous Response Messages. By default the value is 30 seconds. The response message is broadcast to all its RIP enabled interface.[13]
Invalid Timer
The invalid timer specifies how long a routing entry can be in the routing table without being updated. This is also called as expiration Timer. By default, the value is 180 seconds. After the timer expires the hop count of the routing entry will be set to 16, marking the destination as unreachable.[13]
Flush Timer
The flush timer controls the time between the route is invalidated or marked as unreachable and removal of entry from the routing table. By default the value is 240 seconds. This is 60 seconds longer than Invalid timer. So for 60 seconds the router will be advertising about this unreachable route to all its neighbours. This timer must be set to a higher value than the invalid timer.[13]
Holddown Timer
The hold-down timer is started per route entry, when the hop count is changing from lower value to higher value. This allows the route to get stabilized. During this time no update can be done to that routing entry. This is not part of the RFC 1058. This is Cisco's implementation. The default value of this timer is 180 seconds.[13]

Limitations

[edit]
  • The hop count cannot exceed 15, or routes will be dropped.
  • Variable Length Subnet Masks are not supported by RIP version 1 (which is obsolete).
  • RIP has slow convergence and count to infinity problems.[14]

Implementations

[edit]
  • Cisco IOS, software used in Cisco routers (supports version 1, version 2 and RIPng)
  • Cisco NX-OS software used in Cisco Nexus data center switches (supports RIPv2 only[15])
  • Junos software used in Juniper routers, switches, and firewalls (supports RIPv1 and RIPv2)
  • Routing and Remote Access, a Windows Server feature, contains RIP support
  • Quagga, a free open source software routing suite based on GNU Zebra
  • BIRD, a free open source software routing suite
  • Zeroshell, a free open source software routing suite
  • A RIP implementation first introduced in 4.2BSD, routed, survives in several of its descendants, including FreeBSD[16] and NetBSD.[17]
  • OpenBSD introduced a new implementation, ripd, in version 4.1[18] and retired routed in version 4.4.
  • Netgear routers commonly offer a choice of two implementations of RIPv2;[19] these are labelled RIP_2M and RIP_2B. RIP_2M is the standard RIPv2 implementation using multicasting - which requires all routers on the network to support RIPv2 and multicasting, whereas RIP_2B sends RIPv2 packets using subnet broadcasting - making it more compatible with routers that do not support multicasting, including RIPv1 routers.
  • Huawei HG633 ADSL/VDSL routers support passive and active routing with RIP v1 & v2 on the LAN and WAN side.

Similar protocols

[edit]

Cisco's proprietary Interior Gateway Routing Protocol (IGRP) was a somewhat more capable protocol than RIP. It belongs to the same basic family of distance-vector routing protocols.

Cisco has ceased support and distribution of IGRP in their router software. It was replaced by the Enhanced Interior Gateway Routing Protocol (EIGRP) which is a completely new design. While EIGRP still uses a distance-vector model, it relates to IGRP only in using the same composite routing metric. Both IGRP and EIGRP calculated a single composite metric for each route, from a formula of five variables: bandwidth, delay, reliability, load, and MTU; though on Cisco routers, by default, only bandwidth and delay are used in this calculation.

See also

[edit]

References

[edit]

Further reading

[edit]
Revisions and contributorsEdit on WikipediaRead on Wikipedia

Routing Information Protocol

View on Grokipedia
from Grokipedia
The Routing Information Protocol (RIP) is a distance-vector interior gateway protocol (IGP) used to exchange routing information among routers within an autonomous system in IP-based networks, employing hop count as its primary metric to determine the best path to a destination. Designed for small to moderate-sized, homogeneous networks, it limits routes to a maximum of 15 hops, with 16 hops indicating an unreachable destination, to prevent routing loops and ensure efficient convergence. RIP operates over (UDP) on port 520, broadcasting routing updates periodically or in response to changes, making it one of the simplest and oldest protocols still in use. RIP traces its origins to distance-vector protocols used in the during the late 1960s, evolving from the (XNS) developed in the mid-1970s. It was formally standardized by the (IETF) in June 1988 through RFC 1058, which defined the initial version known as RIP-1; this version supported classful networking without masks and used broadcast updates to all interfaces. In November 1998, RFC 2453 introduced RIP-2, enhancing the protocol with support for variable-length masks (VLSM) via an explicit mask field, mechanisms to secure updates, next-hop information to optimize paths, and multicast updates to the address 224.0.0.9 for better efficiency in mixed environments. An version, RIPng, was defined in RFC 2080 in January 1997. These improvements maintained with RIP-1 while addressing key limitations in and security. In operation, RIP routers maintain a and share it with directly connected neighbors, calculating distances by incrementing the hop count from received updates and selecting the lowest-metric route. Despite its simplicity and ease of configuration, RIP's limitations—such as slow convergence times, vulnerability to routing loops in larger topologies, and the fixed 15-hop diameter—make it unsuitable for modern, large-scale networks, where link-state protocols like OSPF are preferred.

History and Development

Origins of Distance-Vector Routing

The concept of distance-vector routing originated in the late 1960s with the , the precursor to the modern , where it served as the original routing algorithm implemented in 1969. Based on the Bellman-Ford algorithm, this approach enabled routers to periodically exchange vectors of distances (metrics) to known networks with their neighbors, allowing each router to compute optimal paths by selecting the lowest-cost route.

Evolution of RIP

The Routing Information Protocol (RIP) traces its roots to the Gateway Information Protocol (GWINFO), developed by Corporation in the mid-1970s as part of the PUP protocol suite for early initiatives to enable efficient routing across heterogeneous networks. This initial version was later adapted as the Routing Information Protocol within the (XNS) in the late 1970s, providing a distance-vector approach for exchanging routing information among gateways. RIP gained prominence through its integration into the Berkeley Software Distribution (BSD) Unix operating system in 1982, where it was implemented as the "routed" daemon to support in TCP/IP environments. This adoption facilitated automated route discovery and maintenance in Unix-based systems, addressing the growing need for straightforward routing mechanisms in small to medium-sized networks amid the early expansion of the and nascent . The protocol's simplicity made it ideal for environments where manual configuration was impractical, promoting its use in academic and research settings. Formal standardization occurred in 1988 with RFC 1058, which documented RIP version 1 (RIPv1) based on the BSD implementation and established it as a for interior gateway routing within autonomous systems. By the late 1980s, RIP had been deployed in key early infrastructures, including networks running BSD Unix and regional connections to the NSFNET backbone, where it handled routing for thousands of hosts across interconnected LANs. Further evolution came in 1998 with RFC 2453, which defined RIP version 2 (RIPv2) under IETF auspices, enhancing compatibility and features while maintaining with earlier deployments.

Core Concepts

Distance-Vector Mechanism

The (RIP) implements the distance-vector routing algorithm, a method where routers periodically exchange routing information with directly connected neighbors to determine the best paths to network destinations based on the hop count metric. In this mechanism, each router maintains a routing table containing entries for reachable networks, the associated distance (number of hops), and the next-hop router toward each destination. Unlike path-vector protocols such as BGP that include full path attributes to explicitly detect loops, RIP prioritizes simplicity by sharing only distance vectors, making it suitable for small to medium-sized autonomous systems where computational overhead must be minimized. The step-by-step update process in RIP operates as follows: each router advertises its complete to all neighboring routers every 30 seconds using UDP port 520. When a router receives such an update from a neighbor, it increments each received metric by one (to account for the additional hop) and compares these values against its own . If the new metric for a destination is lower than the current entry, the router updates its table with the improved route and the neighbor as the next hop; if the metric is equal, it may update based on tie-breaking rules like the age of the route. These changes can trigger immediate propagation to other neighbors to accelerate convergence, ensuring that routing information ripples through the network iteratively until stability is achieved. To prevent routing loops—a common issue in distance-vector protocols where inconsistent updates can cause circular paths—RIP employs specific techniques. Split horizon avoids re-advertising a route back to the neighbor from which it was learned, thereby reducing the risk of loops by not reinforcing potentially faulty information. Poison reverse builds on this by explicitly advertising such routes back to the originating neighbor with an infinite metric of 16, which signals the route as unreachable and helps neighboring routers quickly invalidate it, hastening loop resolution. These methods are applied on a per-interface basis and significantly improve the protocol's robustness without adding complexity. The convergence process in RIP involves the gradual propagation and reconciliation of routing updates across the network, which can be slow due to the periodic nature of exchanges but is mitigated by the loop-prevention features. Consider a simple linear with four routers labeled A, B, C, and D, connected as A—B—C and B—D, where network X is attached to D with an initial metric of 1 from D. Initially, B learns X via D with metric 2, C learns it via B with metric 3, and A via B with metric 3. If the B-D link fails, B marks X as unreachable (metric 16), but without prevention techniques, A might advertise X back to B with its current metric of 3 (based on its outdated path via B), prompting B to increment it to 4 and readopt the route via A; B then advertises this metric of 4 to A and C, leading A to update to 5 via B, and so on, causing the "counting to infinity" problem where metrics escalate (4, 5, ..., 15) over successive updates until all reach 16 and declare X unreachable. With split horizon enabled, B would not advertise X back toward A or C if learned from them, and poison reverse would force B to send metric 16 for X to its neighbors, allowing faster convergence to the correct state where alternative paths (if any, such as a higher-cost C-D link) are adopted or the network is deemed inaccessible. This example illustrates how RIP's distance-vector exchanges enable but rely on bounded metrics (maximum 15 ) to terminate infinite counting.

Hop Count Metric

The hop count metric in RIP represents the distance to a destination network as the number of intermediate routers () that must be traversed along the path. Each router increments the hop count by 1 when processing and readvertising a route received from a neighbor. This simple additive metric prioritizes paths with the fewest , assuming each link has equal , which suits homogeneous, low-latency networks but ignores factors like bandwidth or delay found in more advanced protocols. The protocol defines a maximum valid hop count of 15; any route with a metric of 16 is treated as , signifying the destination is unreachable. This artificial limit prevents indefinite routing loops by ensuring that looped routes eventually reach and are discarded, while also bounding the protocol's applicability to small networks with diameters no larger than 15 .

Protocol Versions

RIP Version 1

Routing Information Protocol Version 1 (RIPv1) was standardized in RFC 1058 in June 1988 by Charles Hedrick of , serving as a specification for exchanging routing information among gateways and hosts in IP networks. This version implements a basic that relies on hop count as the primary metric, with a maximum of 15 hops to prevent routing loops, where a metric of 16 indicates an unreachable destination. RIPv1 exclusively supports classful addressing, meaning it does not include subnet mask information in its routing updates, which assumes all interfaces on a given network share the same mask length as defined by the IP class (e.g., /8 for Class A). Key features of RIPv1 include periodic broadcast updates sent every 30 seconds to the all-ones 255.255.255.255 on broadcast-capable networks, enabling routers to advertise their entire to all devices on the local segment without targeted delivery. It lacks built-in authentication mechanisms, making it vulnerable to unauthorized route injections, and limits each update message to a maximum of 25 route entries to fit within the 512-octet UDP datagram size. These broadcasts ensure compatibility with simple network topologies but contribute to higher network overhead in larger environments. The message format for RIPv1 consists of a fixed 4-byte header followed by variable route entries, each 20 bytes long, allowing up to 25 entries per message. The header includes a 1-octet command field (e.g., 1 for request, 2 for response), a 1-octet version field set to 1, and 2 octets of reserved zeros. Each route entry consists of a 2-octet address family identifier (0002 for IP), 2 octets of reserved zeros, a 4-octet representing the destination network, 8 octets of reserved zeros (unused in Version 1), and a 4-octet metric field encoding the hop count from 1 to 16. Messages are encapsulated in UDP packets using port 520 and transmitted without IP options to maintain simplicity. Operationally, RIPv1's classful design leads to challenges in subnetted environments, as it cannot advertise subnet-specific routes; instead, all subnets of a major network are summarized to the classful boundary when crossing router boundaries. This assumption of uniform subnet masks across networks can result in routing inefficiencies or failures, such as blackholing packets if receiving routers apply incorrect masks to interpret the advertised networks. Border gateways must explicitly filter out subnet routes to prevent propagation issues, limiting RIPv1's scalability in hierarchical or variable-length masked (VLSM) topologies.

RIP Version 2

RIP Version 2 (RIPv2) represents a significant evolution of the original , standardized in RFC 2453 in November 1998 as an . This version extends the protocol defined in RFC 1058 by incorporating mechanisms to support (CIDR) and Variable Length Subnet Masking (VLSM), primarily through the inclusion of subnet mask information within each routing entry in RIP messages. Unlike its predecessor, which assumed addressing and led to inefficiencies in subnetted environments, RIPv2's subnet masks allow routers to advertise and interpret routes with precise network boundaries, enabling more flexible address allocation and reducing fragmentation in modern networks. Key enhancements in RIPv2 include the use of updates sent to the IPv4 address 224.0.0.9 on UDP 520, which improves efficiency by directing updates only to RIP-enabled devices and avoiding unnecessary broadcasts to all hosts on a . Additionally, the protocol introduces route tags, 16-bit fields that enable administrators to mark routes for or to differentiate between internal and external routes imported from other protocols, such as (EGP). For security, RIPv2 supports via a simple password mechanism or keyed-MD5 as defined in RFC 2082, using a reserved Address Family Identifier (AFI) of 0xFFFF in authentication entries to verify message integrity without delving into cryptographic details. To illustrate the benefits of subnet mask support, consider a network divided into of varying sizes, such as a /24 subnet for a department and a /28 for a small office; RIPv2 advertisements include the explicit mask (e.g., 255.255.255.0 for /24), allowing receiving routers to correctly route packets without assuming classful boundaries, thus optimizing path selection and supporting scalable hierarchies in divided environments. Regarding , RIPv2 implementations can interoperate with RIPv1 routers by responding to version 1 requests with classful (mask-omitted) entries and through a configurable compatibility switch that disables advanced features like subnet masks when interacting with legacy devices, though this limits the full utilization of RIPv2 capabilities. This design addresses core RIPv1 limitations, such as the inability to handle subnetted routes accurately, while maintaining deployment feasibility in mixed environments.

RIPng for IPv6

RIPng (Routing Information Protocol Next Generation) is the extension of RIP, standardized in RFC 2080 in January 1997 by Gary Scott Malkin and Robert E. Minnear. It adapts the RIPv2 protocol for networks, using the same distance-vector approach with hop count as the metric (1-15 hops, 16 for unreachable) but addressing -specific requirements. Key features of RIPng include periodic and triggered updates sent every 30 seconds to the all-RIP-routers FF02::9 on UDP port 521, reducing overhead compared to broadcasts. Unlike RIPv2, RIPng does not include in the base specification; instead, it relies on 's built-in security mechanisms, such as the IP Authentication Header (AH) and Encapsulating Security Payload (ESP), for message protection. Route entries support prefixes with an explicit prefix length field (0-128 bits) and include a 16-bit route tag for policy routing, similar to RIPv2. The next-hop address is specified using a dedicated route entry with a metric of 0xFF (255 decimal) if different from the sender. The message format for RIPng consists of a 4-byte header (command, version set to 1 for RIPng, reserved zeros) followed by 20-byte route entries adapted for : a 2-octet AFI (0002 for ), 2-octet route tag, 2-octet prefix length, 2 octets reserved, 16-byte prefix, 8 octets reserved, and 4-octet metric. RIPng is not directly compatible with IPv4 RIP versions, as it operates solely over , but it maintains the core principles of simplicity and is suitable for small to medium networks, though limited by the 15-hop diameter like its predecessors.

Protocol Operation

Message Formats

The Routing Information Protocol (RIP) transmits messages over UDP using port 520 for IPv4 versions and port 521 for RIPng, with each message limited to a maximum size of 512 octets (excluding IP and UDP headers) to accommodate up to 25 route entries. Messages consist of a fixed 4-octet header followed by one or more 20-octet route table entries (RTEs), all encoded in network byte order (most significant octet first). The common header begins with a 1-octet command field, which specifies the type: value 1 indicates a request , used to query a subset or entire from a neighbor, while value 2 denotes a response , which provides information either periodically, in reply to a request, or as a triggered update. This is followed by a 1-octet version field, set to 1 for RIPv1 and RIPv2 or 2 for RIPv2, and 1 for RIPng. The header concludes with 2 octets reserved and set to zero, ensuring alignment and future extensibility. Each RTE in RIPv1 and RIPv2 starts with a 2-octet address family identifier, set to 2 for IP (IPv4), followed by 2 octets reserved and set to zero. The field occupies 4 octets, representing the destination network or host in classful (RIPv1) or classless (RIPv2) format. In RIPv2, this is followed by a 2-octet route tag (for distinguishing internal/external routes), a 4-octet mask (zero if classful), and a 4-octet next-hop (all-zeros to use the message source). The entry ends with a 4-octet metric field, where values 1 through 15 represent hop counts and 16 indicates unreachable (). RIPv1 omits the route tag, mask, and next-hop fields, instead using 12 octets of reserved zeros after the , which limits its support for subnetting. RIPv2 introduces by repurposing the first RTE: if the address family identifier is 0xFFFF (all ones), the subsequent 2 octets specify the authentication type (2 for simple password), followed by 16 octets of data (e.g., a plain-text password padded with nulls). This reduces the maximum RTEs to 24 when is present, as the header and authentication occupy the space of one entry. For RIPng, the RTE structure adapts to IPv6 by using a 16-octet prefix, followed by a 2-octet route tag, a 1-octet prefix length (0-128), and a 1-octet metric (1-15 or 16 for ). Unlike IPv4 RIP, there is no AFI field. A separate 20-octet next-hop RTE type allows specifying an IPv6 link-local next-hop address, with the metric set to 0xFF to distinguish it from standard entries. RIPng does not include in the base format but relies on for security. The binary layout for a RIPv1/RIPv2 response message can be represented as follows, with fields in octets:

0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Command | Version | Reserved (must be 0) | +---------------+---------------+-------------------------------+ | Address Family Identifier (2 for IP) | +-------------------------------+-------------------------------+ | Route Tag (RIPv2 only) | [IP Address](/page/IP_address) (4 octets) | +-------------------------------+-------------------------------+ | Subnet Mask (RIPv2 only, 4 octets) | Next Hop (RIPv2 only, 4 octets)| +---------------------------------------------------------------+ | Metric (1-16, 4 octets, least significant in last octet) | +---------------------------------------------------------------+ (Repeated up to 25 times, or 24 with authentication)

0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Command | Version | Reserved (must be 0) | +---------------+---------------+-------------------------------+ | Address Family Identifier (2 for IP) | +-------------------------------+-------------------------------+ | Route Tag (RIPv2 only) | [IP Address](/page/IP_address) (4 octets) | +-------------------------------+-------------------------------+ | Subnet Mask (RIPv2 only, 4 octets) | Next Hop (RIPv2 only, 4 octets)| +---------------------------------------------------------------+ | Metric (1-16, 4 octets, least significant in last octet) | +---------------------------------------------------------------+ (Repeated up to 25 times, or 24 with authentication)

This structure ensures compatibility between versions when the version field is set to 1, ignoring RIPv2-specific fields. For RIPng, the layout shifts to accommodate the larger prefix while maintaining the 20-octet RTE size.

Routing Update Process

The Information Protocol (RIP) employs a periodic update mechanism where routers broadcast or their entire routing tables to directly connected neighbors every 30 seconds, ensuring that neighboring routers remain synchronized with the network topology. In RIP version 1 (RIPv1), these updates are sent as broadcasts to all devices on the local network, while RIP version 2 (RIPv2) uses multicasts to the address 224.0.0.9, reducing unnecessary traffic to non-router hosts. To prevent synchronization of updates across multiple routers, which could lead to excessive network load, a small random delay of up to 5 seconds is added to the update interval. In addition to periodic updates, RIP supports triggered updates to accelerate convergence after detecting changes in the network, such as link failures or new routes. When a router's is modified—due to a directly connected interface going down or receiving an update with a better metric—it immediately sends a triggered update containing only the affected routes to its neighbors, rather than waiting for the next periodic cycle. This process includes a random delay of 1 to 5 seconds before transmission to avoid "storming," where rapid successive updates overwhelm the network. Triggered updates in RIPv2 may also include route tags to distinguish external routes, aiding in more precise propagation. Upon receiving a RIP update message—formatted as a UDP datagram on port 520—a router follows a structured processing sequence to integrate the information into its routing table. First, the router validates the message by confirming it originates from a valid neighbor and adheres to protocol specifications, such as correct command type (request or response) and version; invalid entries, like those with metrics outside 1-16 or incompatible address families, are discarded. Next, the receiving router increments the advertised metric by 1 to account for the hop cost and applies split horizon by ignoring or poisoning (setting to 16) any route learned from the sender if sending back to that interface. For each valid entry, the router compares the new metric against its current table: if the route is new and the metric is less than 16, it is added; if existing, it updates the entry if the new metric is lower or if the update comes from the current next-hop router (regardless of whether the new metric is the same or higher); routes with metric 16 trigger deletion after a timeout period. This processing ensures gradual propagation of optimal paths based on hop count, with the router potentially issuing its own triggered update if the change affects its table. Consider a simple linear with three routers, A-B-C, where A connects to a destination network X with a metric of 1. Initially, B learns the route to X via A with metric 2, and C learns it via B with metric 3 through periodic updates. If the link between B and C fails, B detects the change and sends a triggered update to A the route to C's networks (metric 16), while C's table times out the route to X after receiving no updates, leading to reconvergence as alternative paths (if any) are discovered—typically within a few update cycles, though full may take up to 90 seconds in larger chains due to the hop-by-hop nature. Conversely, adding a new low-cost link from C to X would trigger C to advertise metric 1 to B, which updates to metric 2 and propagates to A, demonstrating faster convergence for improvements via triggered updates.

Timers and Stability Mechanisms

The Routing Information Protocol (RIP) relies on a set of timers to maintain route validity and facilitate orderly updates across versions including RIP v1, v2, and RIPng. The update timer, defaulting to 30 seconds, governs the periodic transmission of unsolicited routing updates containing the full to neighboring routers, ensuring consistent information dissemination while a random of 0 to 5 seconds (or up to 15 seconds in RIPng) is applied to prevent among multiple routers. When no update for a specific route is received, the invalid —set to 180 seconds by default—expires, marking the route as unreachable and setting its metric to 16 (), which signals potential network changes. This invalidation process triggers route aging, calculated as age = current_time - last_update, where the route remains in the table until further timers elapse. Following invalidation, the garbage-collection —120 seconds—retains the poisoned route in the table while advertising it with metric 16 to inform neighbors of its unavailability, after which the route is fully deleted from the , resulting in a total retention of 300 seconds. These timers collectively ensure graceful route expiration without abrupt disruptions. To enhance stability, RIP incorporates mechanisms such as route , where unreachable routes are explicitly advertised with metric 16 to accelerate convergence by poisoning potential loops, and triggered updates, which are sent immediately upon detecting route changes (e.g., link failures) but delayed by a random 1-5 second interval to curb excessive traffic bursts. These techniques, combined with the timers, prevent count-to-infinity problems during shifts, promoting faster network stabilization without requiring complex computations. In practice, these timers are tunable via configuration commands in RIP implementations, allowing administrators to adjust defaults (e.g., update interval from 10-3600 seconds) based on network size and stability needs, though deviations from standards can risk incompatibility or increased overhead.

Limitations and Improvements

Key Limitations

The Routing Information Protocol (RIP) has several inherent limitations that restrict its use in modern networks. Primarily, it employs a hop count metric capped at 15 hops, with 16 hops signifying an unreachable destination (), which prevents infinite routing loops but confines the protocol to small networks with a diameter no larger than 15 routers. This fixed limit makes RIP unsuitable for large-scale or geographically dispersed autonomous systems. Convergence is another key drawback, as RIP relies on periodic updates every 30 seconds, leading to delays of up to several minutes in propagating changes across the network. The distance-vector nature exacerbates this with the "count-to-infinity" problem, where routers incrementally increase metrics for invalid routes until reaching ; while mechanisms like split horizon (not routes back to the originating neighbor) and poisoned reverse ( invalid routes with infinite metric) mitigate it, they do not eliminate the issue entirely, particularly in complex . Additionally, RIP's update mechanism consumes significant bandwidth by broadcasting or multicasting the entire periodically, regardless of changes, which becomes inefficient in networks with many routers or frequent updates. In RIP , classful addressing further limits flexibility by ignoring masks, complicating deployment in environments using variable-length masking (VLSM). Overall, these constraints render RIP inappropriate for high-speed, large, or dynamic IP networks, where protocols like OSPF or EIGRP offer faster convergence and greater .

Authentication and Security Enhancements

Routing Information Protocol version 2 (RIPv2) introduced mechanisms to protect against unauthorized routing updates, addressing vulnerabilities in the unauthenticated RIP version 1. The protocol supports two primary types: simple password and MD5-based keyed hashing. Simple password , defined in RFC 2453, uses a plain text password transmitted in the authentication data field of the RIP message, making it susceptible to and replay attacks due to its lack of or . In this method, the first route entry in the message has an Address Family Identifier (AFI) of 0xFFFF and an authentication type of 2, with the 16-octet authentication data containing the left-justified password padded with nulls. To provide stronger security, RIPv2 employs keyed hashing as specified in RFC 2082, which uses an type of 3 and incorporates a key identifier, authentication data length, sequence number, and a 16-byte digest in the message. The sender computes the digest by applying the algorithm to the RIP packet header (excluding the authentication data), appending the key, and adding padding and length per RFC 1321; the resulting digest replaces the key in the transmitted packet. Upon receipt, the receiver uses the key identifier to retrieve the corresponding shared key, recomputes the digest, and verifies it against the provided value while checking the sequence number to prevent replays; mismatched digests or outdated sequences cause the packet to be discarded. This mechanism offers protection against both passive eavesdropping and active insertion or modification attacks. For RIPng, the IPv6 adaptation of RIP defined in RFC 2080, security is handled externally through rather than built-in protocol fields. RIPng relies on the IP Authentication Header (AH) for integrity and authentication of routing messages, as outlined in RFC 1826, and optionally the Encapsulating Security Payload (ESP) for confidentiality, per RFC 1827, ensuring that routing updates are protected at the IP layer without modifying the RIPng message format. Best practices for RIPv2 authentication include regular key rotation to mitigate long-term exposure risks, facilitated by configuring multiple keys with overlapping lifetimes for seamless transitions, as supported in RFC 2082. Implementations like those from and enable automated key switching based on configured start times, reducing manual intervention. However, authentication has limitations, including vulnerability to preimage attacks and collisions due to weaknesses in the algorithm, as analyzed in RFC 6039, prompting recommendations to transition to stronger algorithms where possible, though RIP remains constrained to . Despite these enhancements, does not fully address all threats, such as those from misconfigured keys or insider attacks.

Implementations and Usage

Open-Source Implementations

One of the most notable open-source implementations of the Routing Information Protocol (RIP) is , a routing software suite originally developed as a of Zebra project. Quagga provides comprehensive support for RIPv1, RIPv2, and RIPng, enabling distance-vector routing on platforms, including integration with other protocols such as BGP and OSPF for multi-protocol environments. Configuration in Quagga is facilitated through the vtysh , which allows unified management of routing daemons and dynamic updates to the . Although Quagga has seen reduced maintenance in recent years, its codebase remains available through the GNU Savannah repository and is packaged in several distributions, such as and , for legacy deployments. A more actively developed successor to is (FRR), which emerged as a community-driven in 2017 to address and feature stagnation issues in the original project. FRR fully implements RIPv1, RIPv2, and RIPng, with support for in RIPv2 as defined in RFC 4822 for cryptographic authentication and RFC 2082 for simple authentication, helping mitigate unauthorized route injections; for RIPng, security is provided through as recommended in RFC 2082. It also incorporates (VRF) capabilities, allowing RIP instances to operate within isolated routing domains for multi-tenant networks. FRR's modular architecture supports integration with BGP, OSPF, and , and its ongoing development is evidenced by regular releases and contributions via , making it a preferred choice for production and Unix environments. Another prominent open-source option is the BIRD Internet Routing Daemon, designed as a lightweight and efficient alternative for on resource-constrained systems. BIRD supports RIPv1 per RFC 1058, RIPv2 per RFC 2453, and RIPng per RFC 2080, with a focus on deployments through its native handling of multiple routing tables and inter-table protocol filtering. Its modular design emphasizes low overhead, making it suitable for exchange points and IPv6-centric networks where RIPng is used alongside protocols like OSPFv3 and BGP. is actively maintained by the CZ.NIC laboratory and is readily available in major distributions, including and openSUSE, as well as via its official repository. Historically, the GateD (Gateway Routing Daemon) served as one of the earliest open-source implementations supporting , originating from the MERIT project in the 1990s and providing distance-vector routing alongside OSPF and BGP for Unix systems. However, GateD has not received significant updates since the early 2000s and is considered unmaintained, with its codebase preserved in archival repositories such as for educational or legacy purposes rather than active use. Modern open-source RIP implementations like , FRR, and BIRD are typically distributed through package managers in ecosystems, including RPM-based (e.g., ) and Debian-based systems, facilitating easy installation and integration into network stacks.

Commercial and Vendor Support

has provided comprehensive support for both RIPv1 and RIPv2 since the late 1980s, enabling RIP as a core in enterprise routing environments. Configuration options include commands such as ip rip authentication mode [md5](/page/MD5) for securing RIP updates with Message Digest 5 encryption, and auto-summary to control automatic route summarization at network boundaries, which by default aggregates routes into classful network-level routes. This support extends to recent releases like 17.15.x, where RIP remains configurable for IPv4 routing in switches and deployments. Juniper Junos OS offers robust implementation of RIP and RIPng, adhering to key standards such as RFC 2453 for RIPv2 and RFC 2080 for RIPng, with features like UDP port 521 for RIPng multicast updates. RIPng can be integrated into virtual routing instances alongside protocols like OSPFv3, allowing flexible deployment in multi-protocol environments such as service provider edge routers for IPv6 route exchange. Basic configuration involves defining RIP groups, adding interfaces, and applying export policies to advertise routes, supporting its use in smaller-scale or transitional IPv6 networks. In modern networks as of 2025, RIP primarily serves a legacy role in small office/home office (SOHO) and small enterprise setups due to its simplicity, though its adoption has significantly declined since the early 2000s in favor of more scalable protocols like EIGRP and OSPF. Vendor-specific extensions, such as Cisco's support for IP unnumbered interfaces in RIPv2, allow RIP to operate over point-to-point links without dedicating unique IP addresses, conserving address space by borrowing from loopback or other interfaces. This feature facilitates RIP deployment in bandwidth-constrained or address-limited scenarios, though overall usage remains limited to environments where advanced routing demands are minimal.

References

  1. https://datatracker.ietf.org/doc/html/rfc1058
  2. https://www.cisco.com/c/en/us/td/docs/switches/lan/catalyst9600/software/release/17-4/configuration_guide/rtng/b_174_rtng_9600_cg/configuring_rip.pdf
  3. https://courses.cs.duke.edu/spring18/compsci356/slides/11RIP.pdf
  4. https://ipsit.bu.edu/sc546/sc546Fall2002/RIP2/RIP/02.html
  5. https://datatracker.ietf.org/doc/html/rfc2453
  6. https://datatracker.ietf.org/doc/html/rfc2080
  7. https://bitsavers.org/pdf/xerox/xns/standards/XSIS_028112-Internet_Transport_Protocols_198112.pdf
  8. http://www.tcpipguide.com/free/t_RIPOverviewHistoryStandardsandVersions.htm
  9. https://www.livinginternet.com/i/iw_route_igp_rip.htm
  10. https://www.rfc-editor.org/rfc/rfc1058.html
  11. https://www.ntp.org/reflib/papers/bone.pdf
  12. https://datatracker.ietf.org/doc/html/rfc1058#section-2
  13. https://datatracker.ietf.org/doc/html/rfc1058#section-2.1
  14. https://datatracker.ietf.org/doc/html/rfc1058#section-2.2.1
  15. https://datatracker.ietf.org/doc/html/rfc1058#section-2.2
  16. https://datatracker.ietf.org/doc/html/rfc1058#section-2.2.2
  17. https://www.cisco.com/c/en/[us](/page/United_States)/td/docs/ios/iproute_rip/command/reference/irr_book/irr_rip.html
  18. https://datatracker.ietf.org/doc/html/rfc2082
  19. https://datatracker.ietf.org/doc/html/rfc1826
  20. https://datatracker.ietf.org/doc/html/rfc1827
  21. https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/iproute_rip/configuration/15-mt/irr-15-mt-book/irr-cfg-info-prot.html
  22. https://www.juniper.net/documentation/us/en/software/junos/rip/topics/topic-map/rip-authentication.html
  23. https://www.nongnu.org/quagga/
  24. https://www.nongnu.org/quagga/docs/quagga.html
  25. https://docs.frrouting.org/en/latest/ripd.html
  26. https://docs.frrouting.org/en/latest/ripngd.html
  27. https://datatracker.ietf.org/doc/html/rfc4822
  28. https://docs.frrouting.org/en/latest/basic.html
  29. https://frrouting.org/
  30. https://bird.network.cz/?get_doc&v=20&f=bird-6.html
  31. https://bird.network.cz/
  32. https://github.com/pld-linux/gated
  33. https://www.cisco.com/c/en/us/td/docs/ios/iproute_rip/command/reference/irr_book/irr_rip.html
  34. https://www.cisco.com/c/en/us/support/docs/ip/routing-information-protocol-rip/13719-50.html
  35. https://www.cisco.com/c/en/us/td/docs/switches/lan/catalyst9600/software/release/17-15/configuration_guide/rtng/b_1715_rtng_9600_cg/configuring_rip.html
  36. https://www.juniper.net/documentation/us/en/software/junos/standards/topics/concept/rip-ripng.html
  37. https://www.juniper.net/documentation/us/en/software/junos/routing-overview/routing-overview.pdf
  38. https://www.juniper.net/documentation/us/en/software/junos/rip/topics/topic-map/basic-ripng-configuration.html
  39. https://www.exam-labs.com/blog/what-is-rip-routing-information-protocol
  40. https://tolumichael.com/what-are-the-disadvantages-of-rip-over-ospf/
  41. https://community.cisco.com/t5/other-network-architecture-subjects/ip-unnumbered-rip-v2/td-p/190824
Add your contribution
Related Hubs
User Avatar
No comments yet.