03-12-2020 07:09 AM
Hi,
I have two ISPs and I would like to only advertise a specific network on my side to ISP 2 only when ISP 1 is down. Both ISPs only advertise the summarised route of 0.0.0.0/0 in my BGP connection with them. I'm trying to create a conditional advertisement but I'm having issues with the non-exist part as I don't know which network to use in verifying the reach-ability of my ISP 1.
Any help would be greatly appreciated.
Solved! Go to Solution.
03-13-2020 08:03 AM - edited 03-13-2020 08:23 AM
Hello
Using the same prefix for conditional route advertisement using bgp advertised and non-exist maps may not work unless you specify the source ip also, But it should work based on different prefixes in the rib, However given the example below, 0.0.0.0/0 should be advertised if the default from 20.20.20.0/24 doesn’t exist in the route table.
Example:
ip prefix-list 10 permit 0.0.0.0/0
ip prefix-list 11 permit 10.10.10.1/32
ip prefix-list 20 permit 0.0.0.0/0
ip prefix-list 21 permit 20.20.20.1/32
route-map ADV
match ip address prefix-list 10
match ip source-ip prefix-list 11
route-map NO_ADV
match ip address prefix-list 20
match ip source-ip prefix-list 21
router bgp x
neigbour x.x.x. advertise-map ADV non-exist-map NO_ADV
03-13-2020 04:30 AM
Hi,
Post the IP addresses of your ISP's that you use to peer BGP with. Post the prefixes that you want to advertise, and specify which one(s) do you want to advertise conditionally, if which BGP peer fails.
Regards,
Cristian Matei.
03-16-2020 01:34 AM
ISP 1 : 10.10.10.0/30
ISP 2 : 20.20.20.0/30
I would like to advertise 100.100.100.0/24 to ISP 1 only if ISP 2 is down
03-13-2020 07:51 AM
Hello,
based on what you are saying, I wonder if a conditional route works. Since you get only the default route, from both ISPs, that default route will always exist (if one ISP is down, the other still sends the same (default) route). So you cannot match on the only route you get, the default route, because it is always existing.
An alternative would be a simple SLA. When one ISP is down, the route you want to add gets added, if the ISP is back up, the route will be removed. A generic sample config is below:
track 1 ip sla 1 reachability
!
interface GigabitEthernet0/0
description Link to ISP 1
ip address 100.100.100.1 255.255.255.252
ip nat outside
!
interface GigabitEthernet0/1
description Link to ISP 2
ip address 200.200.200.1 255.255.255.252
ip nat outside
!
ip sla 1
icmp-echo 8.8.8.8 source-ip 100.100.100.1
timeout 1000
threshold 2
frequency 3
!
ip sla schedule 1 life forever start-time now
!
event manager applet ROUTE_INJECT_DOWN
even track 1 state down
action 1.0 cli command "enable"
action 2.0 cli command "conf t"
action 3.0 cli command "ip route 150.150.150.0 255.255.255.0 200.200.200.2"
action 4.0 cli command "end"
action 5.0 cli command "clear ip nat translations *"
!
event manager applet ROUTE_INJECT_UP
even track 1 state up
action 1.0 cli command "enable"
action 2.0 cli command "conf t"
action 3.0 cli command "no ip route 150.150.150.0 255.255.255.0 200.200.200.2"
action 4.0 cli command "end"
action 5.0 cli command "clear ip nat translations *"
03-13-2020 08:03 AM - edited 03-13-2020 08:23 AM
Hello
Using the same prefix for conditional route advertisement using bgp advertised and non-exist maps may not work unless you specify the source ip also, But it should work based on different prefixes in the rib, However given the example below, 0.0.0.0/0 should be advertised if the default from 20.20.20.0/24 doesn’t exist in the route table.
Example:
ip prefix-list 10 permit 0.0.0.0/0
ip prefix-list 11 permit 10.10.10.1/32
ip prefix-list 20 permit 0.0.0.0/0
ip prefix-list 21 permit 20.20.20.1/32
route-map ADV
match ip address prefix-list 10
match ip source-ip prefix-list 11
route-map NO_ADV
match ip address prefix-list 20
match ip source-ip prefix-list 21
router bgp x
neigbour x.x.x. advertise-map ADV non-exist-map NO_ADV
03-16-2020 01:42 AM
Hi Paul,
Thanks for your suggestion, I'll try this out.
03-17-2020 01:41 AM
Thanks very much Paul,
Your suggestion worked. I tweaked the config in a few places like on the route map for the non-exist map, I used the "match ip route-source prefix-list xx" command instead.
So thanks for your help.
03-18-2020 08:19 AM
Hi Paul,
I have other networks that I would like to advertise to both ISPs simultaneously, I'd like to know if conditionally advertising one of the networks using the configuration below will affect the other networks as well.
Thanks
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