Routing:
[Gen][CCNA][CCNP Route][CCNP Remote][CCDA][MPLS][EEM][Add][Juniper][ACL][Host]
Switching: [CCNP Switch] [Switch Add] [Intro] [VLANs] [MLS] [STP] [QoS] [Availability] Security: [CCNP Security] [CCNA Security] [CCNP ISCW][PIX] [Adv PIX/ASA] [Net Sec1] [Net Sec2] Wireless: [Wireless] [Wireless Chall] [CCNA Wireless] [Wireless Theory] Voice: [Voice/QoS] [CCNA Voice] [CCVP Gateway] [CCVP Voice] Topics: [Dot1q][Dot1x][BGP][BRI][DHCP][IGRP][IGMP][OSPF][PPP][QoS][RADIUS][RIP][Subnet][SNMP][VLAN] RIPMost routers support RIP and EGP. In the past, RIP was the most popular router protocol standard. Its widespread use is due, in no small part, to the fact that it was distributed along with the Berkeley Software Distribution (BSD) of UNIX (from which most commercial versions of UNIX are derived), and was originally defined in RFC 1058. Unfortunately, it suffers from several disadvantages and has been largely replaced by OSFP and EGB, which have the advantage over RIP in that they can handle large internetworks, as well as reducing routing table update traffic. By default, in RIP, each router transmits its complete routing table to their neighbor once every 30 seconds (although this time is configurable in most routers). CCNA Challenges
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Outline
Most routers support RIP and EGP. In the past, RIP was the most popular router protocol standard. Its widespread use is due, in no small part, to the fact that it was distributed along with the Berkeley Software Distribution (BSD) of UNIX (from which most commercial versions of UNIX are derived), and was originally defined in RFC 1058. Unfor-tunately, it suffers from several disadvantages and has been largely replaced by OSFP and EGB, which have the advantage over RIP in that they can handle large internet-works, as well as reducing routing table update traffic. By default, in RIP, each router transmits its complete routing table to their neighbor once every 30 seconds (although this time is configurable in most routers).
RIP uses a distance-vector algorithm which measures the number of network jumps (known as hops), up to a maximum of 16, to the destination router. This has the disadvantage that the smallest number of hops may not be the best route from source to destination. The OSPF and EGB protocols use a link state algorithm that can decide between multiple paths to the destination router, which are based, not only on hops, but also on other parameters such as delay, capacity, reliability and throughput.
With distance-vector routing each router maintains tables by communicating with neighboring routers. The number of hops in its own table is then computed, as it knows the number of hops to local routers. Unfortunately, the routing table can take some time to be updated when changes occur, because it takes time for all the routers to communicate with each other (known as slow convergence).
RIP packets, which use TCP port 520, generally add to the general network traffic as each router broadcasts its entire routing table every 30–60 seconds. Figure 1 outlines the RIP packet format. The fields are:
- Operation (2 bytes) – this field gives an indication that the RIP packet is either a request or a response. The first 8 bits of the field give the command/request name and the next 8 bits give the version number.
- Network number (4 bytes of IP addresses) – this field defines the assigned network address number to which the routing information applies (note that, although 4 bytes are shown, there are in fact 14 bytes reserved for the address. In RIP version 1 (RIPv1), with IP traffic, 10 of the bytes were unused; RIPv2 uses the 14-byte address field for other purposes, such as subnet masks.
- Number of router hops (2 bytes) – this field indicates the number of routers that a packet must go through in order to reach the required destination. Each router adds a single hop, the minimum number is 1 and the maximum is 16. The maximum number of hops to a destination is thus limited to 15.
- Number of ticks (2 bytes) – this field indicates the amount of time (in 1/18 second) it will take for a packet to reach a given destination. Note that a route which has the fewest hops may not necessarily be the fastest route.
Figure 1 RIP packet format
Configuration
A sample configuration is:
> enable # config t (config)# router ? bgp Border Gateway Protocol (BGP) eigrp Enhanced Interior Gateway Routing Protocol (EIGRP) isis ISO IS-IS iso-igrp IGRP for OSI networks mobile Mobile routes odr On Demand stub Routes ospf Open Shortest Path First (OSPF) rip Routing Information Protocol (RIP) (config)# router rip (config-router)# ? Router configuration commands: address-family Enter Address Family command mode auto-summary Enable automatic network number summarization default Set a command to its defaults default-information Control distribution of default information default-metric Set metric of redistributed routes distance Define an administrative distance distribute-list Filter networks in routing updates exit Exit from routing protocol configuration mode flash-update-threshold Specify flash update threshold in second help Description of the interactive help system input-queue Specify input queue depth maximum-paths Forward packets over multiple paths neighbor Specify a neighbor router network Enable routing on an IP network no Negate a command or set its defaults offset-list Add or subtract offset from RIP metrics output-delay Interpacket delay for RIP updates passive-interface Suppress routing updates on an interface redistribute Redistribute information from another routing protocol timers Adjust routing timers traffic-share How to compute traffic share over alternate paths validate-update-source Perform sanity checks against source address of routing updates version Set routing protocol version (config-router)# version 2 (config-router)# network 166.248.0.0 (config-router)# network 200.169.96.0 (config-router)# network 137.205.232.0 (config-network)# exit