Routers
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Verifying RIP configuration:
Two most common commands used to verify that RIP is properly configured: show ip route & show ip protocols
show ip protocols shows which routing protocols are carrying IP traffic on router.
Most common configurations to verify:
RIP routing is configured
The correct interface are sending and receiving RIP updates
The routing is advertising the correct networks
show ip protocols verify that routes received by RIP neighbors are installed in the routing table
additional commands to check RIP configuration:
show interface interface
show ip interface interface
show running-config
Troubleshooting RIP update issue:
Most of the RIP configuration errors involve an incorrect network statement, discontiguous subnets, or split horizons
debug ip rip finding RIP update issues
debug ip rip displays RIP routing updates as they are sent and received
***The number in ( ) represents the source address encapsulated into the IP header of the RIP update
key indicators to look for in debug ip rip command:
discontiguous subnetworks
duplicated networks can be diagnosed w/ this command
other commands to troubleshoot RIP
show ip rip database
show ip protocols {summary}
show ip route
debug ip rip {events}
show ip interface brief
Preventing Routing Updates through an Interface
Route filtering: regulating the routes that are entered into or advertised out of a route table
Router running distance vector- advertises routes based on what is in the route table, route filter influences which routes the router advertises to its neighbors
Routers running link state protocols- determines route based on information in the link-state database
Route filters have no effect on link-states advertisement or databased
This section only applies to RIP and IGRP
passive interface can prevent routers from sending route updates through a router interface; this prevents other systems on the network from learning about routes dynamically
passive interface stops the router from sending updates to a particular neighbor, but the router continues to listen and use routing updates from that neighbor.
Load Balancing with RIP
Load balancing: concept that allows a router to take advantage of multiple best paths to a given destination
RIP is capable of load balancing over as many as 6 equal-cost path w/ 4 paths being default
"Round robin" load balancing: RIP takes turn forwarding packets over the parallel paths
show ip route can show Equal Cost routes
(*) corresponds to the active route that is used for new traffic
Load Balancing Across Multiple Paths
Load-Balancing: ability of a router to transmit packets to a destination IP address over more than one path.; concept that allows a router to take advantage of multiple best paths to a given destination
paths are derived either statically or dynamically (RIP EIGRP OSPF & IGRP)
The route with the lowest administrative distance is installed in the routing table
Come times the router has to choose one of many routes; it goes with the lowest cost or metric to the destination
Load-balancing can occur when the router receives and installs multiple paths with the same administrative distance and cost to destination; there can be up to 6 equal cost routes some IGP has own limitations EIGRP allows 4
By default most IP route protocols have a max of 4 parallel routes in table; static route always installs 6 (except BGP which allows 1)
The range of max paths is 1-6; to change max number Router(config-router)#maximum-paths [number]
RIP networks must have same hop counts to load balance while IGRP uses bandwidth
Cisco IOS offers two methods of load-balancing
per-packet: if process switching is enabled router will alternate paths
per-destination: packets bound for different host on the same network may use alternate route
*fast switching is enabled only 1 of alternate routes will be cached for destination so all packets will take the same path
Integrating Static Routes with RIP
user defined forcing packets to take a specific path
"specifying gateway of a last resort"- default route
If packet is destined for a subnet not listed in table then sent to default
Router can receive default route through update or generates itself
Static routes can be removed by no ip route
Administrator can override static route w/ dynamic routing information by adjusting the administrative distance value
Each dynamic routing protocol has default administrative distance (AD)
Static route can be undesirable over dynamic route if the AD of static route is higher.
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