bgpd: Derive and set MED from IGP or AIGP

[ton31337]

Related: #17031

[Mark225]

Thank you so much for noticing my request. @ton31337

I have installed and tested this branch with new feature. And, I found a bug about this new added feature. The list of test steps are shown as followed.

1. Built the below topology.

2. Configured the relationships between node.
   n2, n3, n4 --> ISIS, IBGP
   n1-n2 --> EBGP
   n1-n3 --> EBGP
   n4-n5 --> EBGP
   n1 --> AS 1
   n2, n3, n4 --> AS 2
   n5 --> AS 5

3. Set the isis metric between n3 and n4 to 100, while kept the isis metric between n2 and n4 to 10.

4. Set MED from IGP in node n2 and n3, the configuration in n2 is as below.

5. Here, it can be observed that node n1 selects node n2 as next hop to destination 33.0.0.5. It meet the requirements defined in RFC 4451. (33.0.0.5 is the loopback address of n5)
   

6. At this moment, I changed the isis metric between n2 and n4 to 200. However, node n1 still selected node n2 as next hop to destination 33.0.0.5. I think that the change of IGP metric should provoke the change of BGP MED and node n1 should reselect the next hop. But, this didn't seem to be effective.

If possible, could you help solve this problem？

[ton31337]

Could you give the full configs, then I'd test it out?

[Mark225]

Could you give the full configs, then I'd test it out?

Please refer to the followed content. Thank you~

n1's configuration:

!
frr version 10.2-dev
frr defaults datacenter
hostname n1
service integrated-vtysh-config
!
interface eth0
 ip address 10.0.0.1/24
exit
!
interface eth1
 ip address 10.0.1.1/24
exit
!
interface lo
 ip address 33.0.0.1/32
exit
!
router bgp 1
 bgp router-id 10.0.0.1
 neighbor 10.0.0.2 remote-as 2
 neighbor 10.0.1.2 remote-as 2
 !
 address-family ipv4 unicast
  network 33.0.0.1/32
 exit-address-family
exit
!
end

n2's configuration:

!
frr version 10.2-dev
frr defaults datacenter
hostname n2
service integrated-vtysh-config
!
ip prefix-list test seq 5 permit any
!
interface eth0
 ip address 10.0.0.2/24
 ip router isis n2
 isis circuit-type level-2-only
 isis fast-reroute lfa level-2
 isis network point-to-point
exit
!
interface eth1
 ip address 10.0.2.1/24
 ip router isis n2
 isis circuit-type level-2-only
 isis fast-reroute lfa level-2
 isis network point-to-point
exit
!
router bgp 2
 bgp router-id 10.0.0.2
 neighbor 10.0.0.1 remote-as 1
 neighbor 10.0.2.2 remote-as 2
 !
 address-family ipv4 unicast
  redistribute connected
  neighbor 10.0.0.1 route-map test out
 exit-address-family
exit
!
router isis n2
 is-type level-2-only
 net 49.0001.0000.0000.0002.00
 lsp-mtu 1440
exit
!
route-map test permit 10
 match ip address prefix-list test
 set metric igp
exit
!
end

n3's configuration:

!
frr version 10.2-dev
frr defaults datacenter
hostname n3
service integrated-vtysh-config
!
ip prefix-list test seq 5 permit any
!
interface eth0
 ip address 10.0.1.2/24
 ip router isis n3
 isis circuit-type level-2-only
 isis fast-reroute lfa level-2
 isis network point-to-point
exit
!
interface eth1
 ip address 10.0.3.1/24
 ip router isis n3
 isis circuit-type level-2-only
 isis fast-reroute lfa level-2
 isis metric level-1 10
 isis metric level-2 100
 isis network point-to-point
exit
!
router bgp 2
 neighbor 10.0.1.1 remote-as 1
 neighbor 10.0.3.2 remote-as 2
 !
 address-family ipv4 unicast
  neighbor 10.0.1.1 route-map test out
 exit-address-family
exit
!
router isis n3
 is-type level-2-only
 net 49.0001.0000.0000.0003.00
 lsp-mtu 1440
exit
!
route-map test permit 10
 match ip address prefix-list test
 set metric igp
exit
!
end

n4's configuration:

!
frr version 10.2-dev
frr defaults datacenter
hostname n4
service integrated-vtysh-config
!
interface eth0
 ip address 10.0.2.2/24
 ip router isis n4
 isis circuit-type level-2-only
 isis fast-reroute lfa level-2
 isis network point-to-point
exit
!
interface eth1
 ip address 10.0.3.2/24
 ip router isis n4
 isis circuit-type level-2-only
 isis fast-reroute lfa level-2
 isis metric level-1 10
 isis metric level-2 100
 isis network point-to-point
exit
!
interface eth2
 ip address 10.0.4.1/24
 ip router isis n4
 isis circuit-type level-2-only
 isis fast-reroute lfa level-2
 isis network point-to-point
exit
!
router bgp 2
 neighbor 10.0.2.1 remote-as 2
 neighbor 10.0.3.1 remote-as 2
 neighbor 10.0.4.2 remote-as 5
exit
!
router isis n4
 is-type level-2-only
 net 49.0001.0000.0000.0004.00
 lsp-mtu 1440
exit
!
end

n5's configuration:

!
frr version 10.2-dev
frr defaults datacenter
hostname n5
service integrated-vtysh-config
!
interface eth0
 ip address 10.0.4.2/24
exit
!
interface lo
 ip address 33.0.0.5/32
exit
!
router bgp 5
 bgp router-id 10.0.4.2
 neighbor 10.0.4.1 remote-as 2
 !
 address-family ipv4 unicast
  network 33.0.0.5/32
 exit-address-family
exit
!
end

[ton31337]

Tested with your topology and configs, looks good now.

[github-actions]

This pull request has conflicts, please resolve those before we can evaluate the pull request.

[riw777]

looks good