08-20-2008 10:45 PM - edited 03-06-2019 12:56 AM
What is the sequence in which a route processor will decide a the best route to destination?
08-20-2008 10:48 PM
Hi, Look at Route Selection in Cisco Routers
http://www.cisco.com/en/US/tech/tk365/technologies_tech_note09186a0080094823.shtml
I hope this helps.
Best regards.
Massimiliano.
08-20-2008 10:59 PM
Hi,
Please check the scenario :
I have EIGRP & BGP enabled on a router.
Say, S1/0 connects to location A over EIGRP
& S 1/1 connects to location B over BGP.
Location A & Location B are both interconnected via MAN links.
Via S 1/0, only traffic to Location A needs to go & S1/1 should have only Location B traffic though it. In case of failure on one of the links, then there should be an automatic re-routing to reach the other location over MAN links.
Router eigrp as
network x.x.x.x
redistribute static
redistribute bgp AS metric 1000 100 255 1 1500
no auto-summary
!
router bgp AS
bgp log-neighbor-changes
redistribute static metric 1000
redistribute eigrp as metric 1000
redistribute eigrp as route-map traffic
neighbor x.x.x.x remote-as ASS
no auto-summary
!
route-map traffic permit 20
match ip address 35
set metric 500
!
access-list 35 permit x.x.0.0 0.0.255.255
access-list 35 permit y.y.0.0 0.0.255.255
access-list 35 permit z.z.0.0 0.0.255.255
!
Ip route u.u.0.0 255.255.0.0 Serial 1/0
Ip route v.v.0.0 255.255.0.0 Serial 1/0
!
With a configurtaion like this, what would happen? Can my objective be met?
08-21-2008 12:41 AM
Hello Deepa,
In Location B, let the router advertise Location A's network (Create a null route etc). In your router, the Location A route which is received from Location B via BGP, will stay in "r" (RIB Failure) mode and wont be installed in route table since EIGRP has a route already with a better Administrative Distance. Once EIGRP is down, the route to Location A that is waiting in r state will be installed into routing table. We made the redundancy for Location A.
Location B redundancy will be a little bit complex. The reason why is because this time we will require Location A to advertise Location B route via EIGRP externally! (should appear as D EX in your side, so use redistribution in Location A), but since EIGRP has a better AD than BGP, EIGRP will take over instantaneously, which we dont want. So you should apply the following to increase the AD for that D EX route specifically and let the BGP route stay primary.
access-list 10 permit LocationBsubnet LocationBmask
Yourrouter(config-router)#distance 201 x.x.x.x 255.255.255.255 10
x.x.x.x= Is the IP address of Location A EIGRP neighbor
Now Location B route that is advertised from Location A via EIGRP will have an Administrative Distance of 201. Since BGP route which should be the primary route for Location B has an AD of 200, it will be installed into routing table and EIGRP route will stay in topology table and wait BGP route to fail and disappear.
Regards
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