L2VPN BGP signaled VPLS between IOS-XE & Junos - RFC4761

[Jerems]

Hi Guys,

Do you know if a the same MTU value is expected on such topology  between a ISR4321 & a SRX300 to work properly ?

Jun  5 20:25:00.568: XC VFI CFG[VPLS-14121]: Add BGP sig member vpn_id [14121] Local VE[id:41, label:42] Remote VE[id:1, label:262409] L2[mtu:0, cw:Enabled] nh[10.0.0.1]

Jun  5 20:25:00.568: %VFI-4-CONFIG: VFI [VPLS-14121]: BGP signaling next-hop 10.0.0.1 mtu 0 does not match configured VFI mtu 1500

I know that on IOS-XR you can prevent this situation by calling a command like mtu ignore :

l2vpn
autodiscovery bgp
signaling-protocol bgp
mtu mismatch ignore 

What about for ios-xe ?

[Harold Ritter]

Hi @Jerems ,

> Do you know if a the same MTU value is expected on such topology  between a ISR4321 & a SRX300 to   > work properly ?

Yes, this is indeed expected.

The MTU is just exchanged as part of the signalling and has no bearing on the data plane.

Default on the Juniper side is to set it to zero, unless it is explicitly set.

https://www.juniper.net/documentation/us/en/software/junos/ex9200-vpn-l2/vpn-l2/topics/task/vpns-layer2-mtu-configuring.html

> I know that on IOS-XR you can prevent this situation by calling a command like mtu ignore :

I do not think this command is available on IOS-XE. 

The way to fix the issue could be to set the MTU value on the SRX to what is expected by the IOS-XE side.

Regards,

[Jerems · Accepted solution]

Hi @Harold Ritter,

I finally found my way through this VPLS setup using BGP autodiscovery and signaling on IOS-XE & Junos

So, as a summary :

• Disabling Control-Word on both side did the trick.
• Setting up a MTU value on Juniper side did not help, eventhough the following message might lead to troubles, it did not affect my setup actually.

Here is the working config on the juniper :

set routing-instances vpls-14121 protocols vpls site 1 interface ge-0/0/5.21
set routing-instances vpls-14121 protocols vpls site 1 site-identifier 1
set routing-instances vpls-14121 protocols vpls site-range 100
set routing-instances vpls-14121 protocols vpls no-tunnel-services
set routing-instances vpls-14121 protocols vpls vpls-id 14121
set routing-instances vpls-14121 protocols vpls mtu 1514
set routing-instances vpls-14121 protocols vpls ignore-encapsulation-mismatch
set routing-instances vpls-14121 interface ge-0/0/5.21
set routing-instances vpls-14121 description "BGP Signaled VPLS"
set routing-instances vpls-14121 instance-type vpls
set routing-instances vpls-14121 vlan-id 21
set routing-instances vpls-14121 route-distinguisher 10.0.0.1:21
set routing-instances vpls-14121 vrf-import L2Vpn-vpls-14121-Import
set routing-instances vpls-14121 vrf-export L2Vpn-vpls-14121-Export

And on the Cisco :

l2vpn vfi context VPLS-14121 
 vpn id 14121
 mtu 1500
 l2protocol forward
 autodiscovery bgp signaling bgp 
  ve id 41
  ve range 100
  rd 10.0.0.41:21
  route-target export 65003:21
  route-target import 65003:21
!
bridge-domain 21 
 member GigabitEthernet0/0/1 service-instance 21
 member vfi VPLS-14121
!
interface GigabitEthernet0/0/1
 no ip address
 negotiation auto
 service instance 21 ethernet
  encapsulation dot1q 21
 !
!

At some times i also mixed the configuration at each side :

"control-word exclude" or "no control-word" helped a lot .

I can provide packet-capture if needed.

Regards,

Jerems

[Jerems]

I will refine the junos config as some of the statements are maybe not mandatory.

[Harold Ritter]

Glad you could fix the issue @Jerems  and thanks for the feedback. I am sure it will be helpful to others as well