I have a litle bug in my lab with 3 routers and would like to share this bug with you :-)
3x Equiment 3550
ios version: 12.1(14)EA1a
system image: c3550-i5q3l2-mz.121-14.EA1a/c3550-i5q3l2-mz.121-14.EA1a.bin
we want to advertise dynamicaly the default route from the Internet router, thru a firewall, to a internal router which run ospf. Protocol use between routers is bgp.
And actually,it work well as sons as both router see each others. The internal router run bgp/ospf and have a "default information orginate" to advertise the default route with all the internal network.
Internet router Bgp
Firewall (tcp/udp 179 open)
Internal route A bgp/ospf
Internal router B ospf (ditribution layer)
The problem is when I stop the firewall to close the bgp connection's (it force de default route to another Internet access on the network).
I wait for about 3 min for bgp update and the Internal router A should remove the default route in his database and should "stop" annoncing the default router to everyone (router B).
For some reason .. it doesnt work .. router B keep receiving info that router A is the default route. To make it work, I must manually do a "clear ip ospf process" then router B converge to another router for the default route.
Internet router config:
Router bgp 65535
neighbor 18.104.22.168 remote-as 65535
ip route 22.214.171.124 255.255.255.255 to -> firewall
router ospf 1
default-information originate route-map exist
access-list permit 1 internet segement of the internet router
If the other route is a BGP route, then you're probably hitting a problem with the preference of BGP and OSPF routes. There's a quirk where the admin distance is ignored in certain orders of operation, and a BGP route is preferred in the table over other routes.
So, it's probably not a bug, it's probably just normal behaviour. You could try setting your eBGP distance higher than your OSPF distance--set eBGP and iBGP both to 200, say, and see if that helps.
When the link between a pair of Internet/internal router Does you BGP session remains up?
You should probably set the ebgp-multihop to be no greater than 2 (just the required value to traverse the FW).
If any part of the link between the Internet/internet router goes down (physical interface, cable, switch, FW, etc) the BGP session should go down and therefore you shouldn't have to choose between two prefixes learnt from two different routing protcols on the router A since the no BGP routes will be available at this point.
Let me know if I make sense,
Harold Ritter Sr. Technical Leader CCIE 4168 (R&S, SP) email@example.com México móvil: +52 1 55 8312 4915 Cisco México Paseo de la Reforma 222 Piso 19 Cuauhtémoc, Juárez Ciudad de México, 06600 México
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