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RIP and IGRP
- Routing Information Protocol (RIP) and Interior Gateway Routing Protocol (IGRP) are DV
routing protocols. Both are designed for small networks and have many similarities. The main
advantage of IGRP over RIP is it provides a better measurement when determining the best
route, and better scalability (overcomes the limitation of RIP maximum hop count – 15).
- Metric is the distance to a remote or destination network.
- RIP uses only hop count to determine the best route to a subnet. If there are multiple routes to a
same network with the same hop counts, RIP can perform load balancing over those equal-cost
links. The total number of equal-cost routes that can be included in the routing table can be
changed with the maximum-paths {num} router subcommand (max of 6, default is 4).
- Pinhole congestion is a problem scenario where RIP treats links with different bandwidth or
speeds (T1 vs. 56K dial up) as equal cost due to same hop count – the main disadvantage of RIP.
- IGRP is a Cisco-proprietary DV routing protocol, which means all routers must be Cisco
routers in order to use IGRP as the routing protocol throughout the network.
- IGRP uses multiple factors in determining the best path to a remote network. By default, IGRP
composite metrics are calculated via a function based on the bandwidth and delay of the link.
The reliability and load utilization can also be used; whereas the MTU size is never been used.
- The unit of bandwidth is kbps.
Ex: bandwidth is defaults to 1544 on serial interfaces. (1544kbps = 1.544Mbps = T1 speed)
- RIP is only able to load balance over paths with the same hop count (equal cost paths) whereas
IGRP is able to load balance over unequal cost paths (unequal metric load balancing).
The variance router subcommand configures IGRP load balancing over unequal cost paths.
- Cisco routers perform 2 types of load balancing over parallel paths in a round robin basis.
Each type has its own pros and cons.
Round robin on the per-packet basis
(Process Switching)
Round robin on the per-destination or
per-session basis (Fast Switching)
The router simply takes turn when selecting the
path for sending packets. This option provides
the most even distribution across parallel paths
but does not preserve packet order.
The router distributes packets based on the
destination address (all packets for Host1 go over
first path, all packets for Host2 go over second
path, etc). This option preserves packet order.
- Below compares RIP and IGRP features with their default values:
Feature RIP IGRP
Metric Hop count Bandwidth, delay, reliability, and load utilization.
Update Timer 30 seconds 90 seconds
Invalid Timer 180 seconds 270 seconds (3 x update timers)
Holddown Timer 180 seconds 280 seconds (3 x update timers + 10 seconds)
Flush Timer 240 seconds 630 (7 x update timers)
Triggered Updates Yes Yes
Infinite Metric 16 4,294,967,295
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