02-05-2010 10:28 AM - edited 03-04-2019 07:25 AM
Hello
can someone suggest on the design. we had some issues recently
Customer site A
ISP-WAN-R1,ISP-WAN-R2, CUSt-WAN-R1 and CUSt-WAN-R2 run ospf and have their own area , area 0
CUST-WAN-R1, CUST-WAN-R2, CUST-LAN-6509A and CUST-LAN-6509B run ospf and have their own area , area 0
6509A and 6509B have networks 10.1.0.0 and 191.1.0.0. they are annouced using ospf by them
CUST-WAN-R1 and CUST-WAN-R2 learn about these networks
CUST-WAN-R1 and CUST-WAN-R2 with thier OSPF running send infor about network 10.1.0.0 and 191.1.0.0 to ISP-WAN-R1 and ISP-WAN-R2
ISP-WAN-R1 and ISP-WAN-R2 have EBGP configured and they send these routes into MPLS cloud to reach customer site b and customer site c
ISP-WAN-R1 and ISP-WAN-R2 should send routes of customer site b and c to
At customer site B and customer site C, there is similar set up to Customer site A
what is requried is no load balancing but have a primary path as shown in the attachment and have a backup path
how should OSPF be configured at all customer sites?
how should BGP be configured on ISP WAN routers at all sites?
there was issue recently when both CUST-WAN-R1 and CUST-WAN-R2 stopped sending traffic to 10.1.0.0 and 191.1.0.0
both these routers were not learning them from CUSt-WAN-R1 and CUSt-WAN-R2 via ospf but in thier routing table there was EBGP with AD 20/0 for 10.1.0.0 and 191.1.0.0
Solved! Go to Solution.
02-06-2010 02:10 AM
Hello Followyourself,
>> how should OSPF be configured at all customer sites?
how should BGP be configured on ISP WAN routers at all sites?
BGP routes should be redistributed into OSPF using OSPF O E1 external route type with an higher seed metric on less preferred path.
router ospf 10
redistribute bgp 10 subnets type 1 route-map setmetric
route-map setmetric
set metric 50
on second router:
router ospf 10
redistribute bgp 10 subnets type 1 route-map setmetric2
route-map setmetric2
set metric 5000
My guess is that your recent issue was caused by mutual redistribution between OSPF and BGP done on border routers.
This should be avoided or handled in the correct way: having two border routers you would have two different ASBR.
BGP allows to advertise networks with network command if they are known in the IP routing table by any mean including OSPF
under router bgp:
remove redistribute OSPF if present and use
network commands, match some component routes exactly including their actual subnet mask
example if there is a 10.1.15.16/28 prefix in IP routing table to match it you should use:
network 10.1.15.16 mask 255.255.255.240
you can create aggregate prefixes if desired with aggregate-address only command:
aggregate-address 10.1.0.0 255.255.0.0 summary-only
the component route above is not sent to eBGP neighbor only the aggregate 10.1.0.0/16.
if all component routes of net 10.1.0.0/16 disappear from IP routing table and then from BGP table the router will withdraw the advertisement of the aggregate address.
Doing this in all sites should avoid undesired re-injection from MPLS cloud of local networks on eBGP sessions.
Hope to help
Giuseppe
02-05-2010 04:56 PM
The part you're describing in the last semtence is very common in BGP / OSPF MPLS environments. eBGP routes have an AD of 20, OSPF routes have an AD of 110. Therefore, eBGP routes are preferred and the traffic gets routed back to the MPLS cloud rather than taking OSPF.
The easy way to fix this is "BGP backdoor", which will change the AD to 200. OSPF routes will then be preferred.
02-06-2010 02:10 AM
Hello Followyourself,
>> how should OSPF be configured at all customer sites?
how should BGP be configured on ISP WAN routers at all sites?
BGP routes should be redistributed into OSPF using OSPF O E1 external route type with an higher seed metric on less preferred path.
router ospf 10
redistribute bgp 10 subnets type 1 route-map setmetric
route-map setmetric
set metric 50
on second router:
router ospf 10
redistribute bgp 10 subnets type 1 route-map setmetric2
route-map setmetric2
set metric 5000
My guess is that your recent issue was caused by mutual redistribution between OSPF and BGP done on border routers.
This should be avoided or handled in the correct way: having two border routers you would have two different ASBR.
BGP allows to advertise networks with network command if they are known in the IP routing table by any mean including OSPF
under router bgp:
remove redistribute OSPF if present and use
network commands, match some component routes exactly including their actual subnet mask
example if there is a 10.1.15.16/28 prefix in IP routing table to match it you should use:
network 10.1.15.16 mask 255.255.255.240
you can create aggregate prefixes if desired with aggregate-address only command:
aggregate-address 10.1.0.0 255.255.0.0 summary-only
the component route above is not sent to eBGP neighbor only the aggregate 10.1.0.0/16.
if all component routes of net 10.1.0.0/16 disappear from IP routing table and then from BGP table the router will withdraw the advertisement of the aggregate address.
Doing this in all sites should avoid undesired re-injection from MPLS cloud of local networks on eBGP sessions.
Hope to help
Giuseppe
02-06-2010 04:17 AM
thanks for the reply and explanation
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