ASR920 BGP on BDI interface doesn't work

[spadhausen]

Hello, I have a big issue:

ASR920 with 2x 10GBe on a port channel to my uplink (0.0.0.0) and BGP running OK

2x10GBe on a port channel where I receive qnq vlans.

I have created a BDI interface, I can ping the remote ends with no issue.

The issue is that I cannot reach via telnet nor run BGP on the BVI.

I set a /30 ip on the BDI, I can ping and trace the remote end (no ACL, no filters, nothing). I cannot telnet the remote end, nor BGP.

Is there a limitation of the BGP functionality on BDI interface on ASR920?

ASR920MIX#sh ver
Cisco IOS XE Software, Version 17.06.02
Cisco IOS Software [Bengaluru], ASR920 Software (PPC_LINUX_IOSD-UNIVERSALK9_NPE-M), Version 17.6.2, RELEASE SOFTWARE (fc7)
Technical Support: http://www.cisco.com/techsupport
Copyright (c) 1986-2021 by Cisco Systems, Inc.
Compiled Tue 23-Nov-21 10:17 by mcpre

ROM: 15.6(48r)

ASR920MIX uptime is 9 weeks, 1 day, 21 hours, 39 minutes
Uptime for this control processor is 9 weeks, 1 day, 21 hours, 46 minutes
System returned to ROM by reload at 23:05:24 ITALY Thu Dec 19 2024
System restarted at 15:04:46 ITALY Fri Dec 20 2024
System image file is "bootflash:asr920-universalk9_npe.17.06.02.SPA.bin"
Last reload reason: PowerOn

License Level: advancedmetroipaccess
License Type: Permanent
Next reload license Level: advancedmetroipaccess

Smart Licensing Status: Smart Licensing is DISABLED

cisco ASR-920-4SZ-A (Freescale P2020) processor (revision 1.0 GHz) with 864646K/6147K bytes of memory.
Processor board ID CAT2230U0TC
2 Gigabit Ethernet interfaces
4 Ten Gigabit Ethernet interfaces
32768K bytes of non-volatile configuration memory.
3670016K bytes of physical memory.
1231647K bytes of eMMC flash at bootflash:.

I have also tried to create a loopback interface and run BGP from there, with no success.

==========================================

interface Loopback1
description virtual interface for BGP
ip address 100.80.2.110 255.255.255.255
no ip redirects
no ip proxy-arp
!
interface Port-channel2
mtu 9000
no ip address
no ip redirects
no ip proxy-arp

service instance 306 ethernet
encapsulation dot1q 306 second-dot1q 10
rewrite ingress tag pop 2 symmetric
bridge-domain 11 split-horizon group 0

interface BDI11
ip address 100.80.5.1 255.255.255.252 
no ip redirects
no ip proxy-arp
!

TEST: If I set the remote neighbour 100.80.5.2: doesnt work, the peer is DIRECTLY CONNECTED

If I set a remote loopback on the remote device and set a static route, DONT WORK

If I remove the static route and the path to the remote loopback address goes through wan with another route, works.

The are NO FILTERS, just a bunch of qnq in the port-channel2

Seems that when traffic goes through BDI it doesnt work.

[paul driver]

Hello
nw - either case the fact is- you need to have tcp reachability and you do not have that as such BGP should never come up.
So to answer your initial QP question - it isn’t bgp over BDI its tcp reachabilty over it and once you’ve sorted that - maybe change your encapsulation etc.. and you gain tcp reachabilty then i’m quite sure bgp will work 

[spadhausen]

Hello. I have tcp reachability since if i manually set a default route on the remote endpoint. Everthing routes correctly.

[paul driver]

Hello

---

@spadhausen wrote:
I have tcp reachability since if i manually set a default route on the remote endpoint. Everthing routes correctly.

---

Then as stated previously BGP doesn't like default routes for establishing peerings.
It needs to be either directly connected,specific static or dynamic igp route entrys for the associated peering address otherwise bgp will not form and this is to negate any possible route flapping and/or routing loops, so in summary its recommended not to use any default routes for any potential bgp peer

[spadhausen]

I wanted to say that we have tcp reachability complete, it is like a cable!
If on the remote end I set a default route, I can route freely through the cisco router.
The BGP session doesnt come up. It is on a /30 !
I dont know, sorry, If I am not good at explaining things or else ☹

[paul driver]

---

@spadhausen wrote:
I wanted to say that we have tcp reachability complete, it is like a cable!
If on the remote end I set a default route, I can route freely through the cisco router.

The BGP session doesnt come up. It is on a /30 !

---

Maybe the directly connect interface is on a /30 but you are not peering with that you have stated your peering with a loopback  and that is reachable via a default route so if this is correct its more than likely bgp will NOT establish.

[spadhausen]

Hello Paul, 

I have writtend that I did multiple test, with loopback (multihop) and without loopback, directly connected.

Are we sure 100% that is not a feature limitation on the ASR920 BGP on the BDI ?

[paul driver]

Hello
I am not going to say 100% , As im still unlcear how you've set that BDI up,.

However ...you are saying no tcp reachability UNLESS you use a default route but as ive started numerous times  BGP will/should NOT establish on a default route which im quite sure about plus its advisable not to use one.

So if the above is correct then you have a transit issue over BDI for tcp reachability ( when NOT using a default route)

[spadhausen]

Hello.

Look at my diagram, please. Dont misunderstand me, I know how bgp works and how to configure it, but I opened this post because IT DOESNT WORK as It is supposed to work.

On the BDI, I have set a /30... at the remote end there is a mikrotik router. I can ping/trace him correctly but DOESNT establish any sessions. no packet received at the MT side.

If I replace the CISCO with the MT, the BGP works immediately, very very same configuration.

If I set a static IP of the /30 on the remote part (100.80.5.2/30 and set as default gw 100.80.5.1 (the cisco), the traffic flows, but I am without BGP.

The original question is:

Are there any specific limitation on ASR920 and BDI interfaces? Does BGP run there? I cannot even start e telnet session from the cisco 100.80.5.1/30 to the remote end 100.80.5.2/30 that goes timeout, but ping/traceroute is ok.

[paul driver]

Hello


As for this

---

@spadhausen wrote:
I replace the CISCO with the MT, the BGP works immediately, very very same configuration.

If I replace the CISCO with the MT, the BGP works immediately, very very same configuration.

---

This is a Cisco forum not an MT one so just because it works with another vendor doesn't necessarily mean it will would with Cisco, however saying that as far as I am aware there is no limitation for bgp on ASRs rtrs running BDI as long as you adhere to cisco recommendations on the practises of BDI and BGP..

[spadhausen]

Hello Paul.

Thank you for your answer.

Trying to simplify:

one BDI interface, with a /30 IP on it.

I am not able to start a BGP session with the peer (100.80.5.1 to 100.80.5.2)

It is a VERY SIMPLE BGP scenario into a point-to-point link /30

No filter, nothing, Another vendor works on a /30, the Cisco not, the only parameter is the BDI interface.

[paul driver]

Hello
this is where i’m confused with you topology - to bridge an interface you don’t really require a BDI routed interface its optional to be honest - you just need to bridge the physical interface north/south of the wan rtr 

example-
Home xdsl pppoe rtr default set to routed mode - now i want to use that rtrs wan ip address and apply it to my own rtr attach behind the dsl rtr - what i can do is set the xdsl rtr in bridge mode and then use it ip on my own rtr

This is basically what i think you should be doing here but using BDI instead of IRB but it seems your not 

[spadhausen]

On the metro eth I have multiple remote offices. At the moment we have a mikrotik router and a lot of /30 with BGP there.

I would like to replace the cisco in the same scenario but I have seen that I am not able to run anything on the BDI.

[MHM Cisco World]

You not reply to my comment do you use default route in both side?

MHM

[spadhausen]

Sorry I was from the mobile phone.

I have a default route from the juniper through a successfully established BGP connection, directly on a /29.

From the metro eth I have a /30 to the remote IP (directly connected). I am not able to do BGP in the /30 on the BDI.

[Georg Pauwen]

Hello,

since this post is getting very long, I am not sure what and what not has already been asked. Is the BDI reachable from the Juniper WITHOUT BGP ? You might want to check BGP timers, as well as MTU settings on both the BDI as well as the Juniper (should be the default 1500, but make sure that is actually configured).