As he mentioned above, I don't believe he will be receiving a default route from the service provider that he can pass in via redistribution, so an option available is to use the bgp "default-information originate route-map command he mentioned". I've used this in combination with IP Sla probes and tracking recently to get the conditional announcement, and base it upon upstream reachibility since in my case its rare that line protocol on the isp circuit goes down since there is an on-site service provider switching equipment. I've used icmp probes for this, but those tend to get dropped from time to time, I've found a tcp connect probe to port 80 on some well known web sites seems to work pretty well at least for me. What i did was tied up a bogus static route to a particular ip address and tied a sla tcp connect to this, this static route is then referenced by the default-information route map, so when the tcp connect fails, bgp pulls the default route out. It looked liked this:
! ! track 2 rtr 2 reachability delay down 10 up 120 ! ! ! router bgp 65501 no synchronization bgp router-id 10.255.255.254 bgp log-neighbor-changes neighbor 10.255.255.252 remote-as 65500 neighbor 10.255.255.252 description *** eBGP Peering to HQ Switch 1 *** neighbor 10.255.255.252 password 7 supersekret neighbor 10.255.255.252 ebgp-multihop 2 neighbor 10.255.255.252 update-source Loopback0 neighbor 10.255.255.252 default-originate route-map CONDITIONAL_DEFAULT_ORIGINATE neighbor 10.255.255.252 soft-reconfiguration inbound no auto-summary ! ip route 1.1.1.1 255.255.255.255 Null0 name Used_For_BGP_Default_Originate_DO_NOT_REMOVE track 2 ip route 0.0.0.0 0.0.0.0 upstreamisp ! ! ! ip prefix-list TRACKED_ROUTE seq 5 permit 1.1.1.1/32 ! ip sla logging traps ip sla schedule 1 life forever start-time now ip sla 2 tcp-connect 209.191.93.52 80 source-ip myipaddress source-port 52142 control disable timeout 5000 frequency 10 ip sla reaction-configuration 2 react timeout threshold-type consecutive 2 action-type trapOnly ip sla schedule 2 life forever start-time now ! ! route-map CONDITIONAL_DEFAULT_ORIGINATE permit 10 match ip address prefix-list TRACKED_ROUTE Keep in mind, if you have an iBGP adjacencies between the two routers, and one of the routers is losing it's ebgp default route, and is now preferring that default route via ibgp via the internal peering AND doing redistribution into an IGP ie OSPF then you must use the BGP redistribute internal, bgp process level command. This is in specific scenarios. HTH, Nick Griffin On Sat, Jan 31, 2009 at 12:50 PM, Pete S. <[email protected]> wrote: > I'd imagine you aren't completely redistributing your bgp tables into > OSFP, and from your diagram I'll assume you are doing ibgp between > your edge routers already. So build a prefix list, and route-map, > which permits only the default route from bgp. Redistribute the bgp > process into ospf, based on that route-map, as an E1 type. This will > put the default into your ospf area, and traffic will flow towards the > closest exit. If you rather a primary/secondary, use the ospf E2 type > and assign a large metric to your secondary. > > I haven't checked the syntax, but this should probably point you in > the right direction. > > !On your BGP routers > ! > ip prefix-list bgp_default->ospf seq 5 permit 0.0.0.0/0 > ip prefix-list bgp_default->ospf seq 100 deny 0.0.0.0/0 ge 1 le 24 > ! > route-map bgp->ospf permit 10 > match ip address prefix-list bgp_default->ospf > ! > router ospf 100 > ! I assign an arbitrary site ID, and then prepend my AS onto it but > whatever suits you, tag is optional > ! select your own metric-type and metric depending on the exit > behavior you want. > redistribute bgp 65535 metric-type 2 metric 100 tag 6553501 > route-map bgp->ospf > ! > ! > > > > --Pete > _______________________________________________ > cisco-nsp mailing list [email protected] > https://puck.nether.net/mailman/listinfo/cisco-nsp > archive at http://puck.nether.net/pipermail/cisco-nsp/ > _______________________________________________ cisco-nsp mailing list [email protected] https://puck.nether.net/mailman/listinfo/cisco-nsp archive at http://puck.nether.net/pipermail/cisco-nsp/
