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Ask the Expert- SD-WAN

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Beginner

Re: BGP - 3 isps, 1 router doesn't want to play nicely..

Actually I ended up using policy based routing. As I needed to control the traffic based upon the "source" address, not the destination. I needed certain subnets on my network to be routed thru certain isps.

One question about the next-hop-statement that i used. It seems you can add more then one next-hop.

set ip next-hop 209.120.155.13 etc..

Does the 2nd next-hop only go into affect if the 1st one is unreachable?

Since I have bgp running, and if the first one is unreachable, will the packets be automatically sent to the other routers? or Do i need to specify the other routers as next-hop?

Thanks.

-GK

Rising star

Re: BGP - 3 isps, 1 router doesn't want to play nicely..

The 2nd next hop is used if the first next hop is unreachable (not in the routing table). The next hop would normally be learned through an IGP (connected, static, etc), rather than through BGP (?), but once this route was removed from the table, the second next hop would be used.

Russ.W

Beginner

Re: BGP - 3 isps, 1 router doesn't want to play nicely..

If it runs out of next-hop, but it has bgp neighbors, will it send the packet to one of them?

-GK

Rising star

Re: BGP - 3 isps, 1 router doesn't want to play nicely..

In other words, if you do a match, then set the next hop, and none of the next hops exist, will it revert to normal routing? Yes, it will. If there is a route in the routing table, and the set next-hop fails, the router will then use the route in the routing table.

For instance:

access-list 101 permit ip host 208.0.9.12 any

!

route-map testnexthop permit 10

match ip address 101

set ip next-hop 1.1.1.1

!

interface Serial0/3

ip address 208.0.14.13 255.255.255.0

ip policy route-map testnexthop

!

2651C#ping

Protocol [ip]:

Target IP address: 208.0.10.1

Extended commands [n]: y

Source address or interface: 208.0.9.12

Type escape sequence to abort.

Sending 5, 100-byte ICMP Echos to 208.0.10.1, timeout is 2 seconds:

.....

Success rate is 0 percent (0/5)

2651D#

2w4d: IP: s=208.0.9.12 (Serial0/3), d=208.0.10.1, len 100, policy match

2w4d: IP: route map testnexthop, item 10, permit

2w4d: IP: s=208.0.9.12 (Serial0/3), d=208.0.10.1 (Serial0/0), len 100, policy rejected -- normal forwarding

So, the set next-hop fails, and 26D falls back to the routing table, where the actual destination is directly connected.

Russ.W

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