[ncs 5500] 4-byte ASN

[Carlos A. Silva]

Hi, 

I'm currently testing eBGP in an NCS5500. While a 2-byte ASN session worked without a problem, the 4-byte session did not (against Spirent TG). We get the following error messages:

nt=3071, memfailcount=0}}
RP/0/RP1/CPU0:Feb 28 18:10:31.462 : bgp[1050]: [default-rtr]: Received UPDATE from 10.0.3.5 (length incl. header = 96)
RP/0/RP0/CPU0:Feb 28 18:10:31.462 : bgp[1050]: [default-rtr]: NH-Validate-Create: addr=10.0.3.5/32, len=4, nlriafi=0, nbr=10.0.3.5, gwafi=0, gwlen=4, gwaddrlen=32::: nhout=0x0x7ffbb43a234c, validity=1, attrwdrflags=0x00000000
RP/0/RP0/CPU0:Feb 28 18:10:31.462 : bgp[1050]: [default-rtr]: Ignoring NEW_ASPATH attribute from 10.0.3.5 (a 4-byte AS capable peer)
RP/0/RP0/CPU0:Feb 28 18:10:31.462 : bgp[1050]: [default-rtr]: --bgp4_rcv_attributes--: END: nbr=10.0.3.5:: msg=0x0x2217ca8/96, updlen=77, attrbl=0x0x2217cbf/33, ipv4reachlen=40, msginpath=0x0x7ffbb9fb37c0, asloopcheck=1, attrwdrfl=0x00000000:: samecluster=0, local_as_prepended=0, attr_wdr_flags 0x00000000, myascount=0:: rcvdata=0x0x2217ce0/0, errptr=0x0x2217cd3/13
RP/0/RP0/CPU0:Feb 28 18:10:31.462 : bgp[1050]: [default-rtr] (ip4u): Received unreachables from 10.0.3.5: attrcode=0, attrwdrflags=0x00000000
RP/0/RP0/CPU0:Feb 28 18:10:31.462 : bgp[1050]: [default-rtr] (ip4u): UPDATE from 10.0.3.5 with attributes:
RP/0/RP0/CPU0:Feb 28 18:10:31.

RP/0/RP1/CPU0:Feb 28 18:10:31.461 : bgp[1050]: [default-rtr]: --bgp4_rcv_attributes--: END: nbr=10.0.3.5:: msg=0x0x184f5d8/96, updlen=77, attrbl=0x0x184f5ef/33, ipv4reachlen=40, msginpath=0x0x7fa7761ad7c0, asloopcheck=1, attrwdrfl=0x00000000:: samecluster=0, local_as_prepended=0, attr_wdr_flags 0x00000000, myascount=0:: rcvdata=0x0x184f610/0, errptr=0x0x184f603/13
RP/0/RP1/CPU0:Feb 28 18:10:31.461 : bgp[1050]: [default-rtr] (ip4u): Received unreachables from 10.0.3.5: attrcode=0, attrwdrflags=0x00000000
RP/0/RP1/CPU0:Feb 28 18:10:31.461 : bgp[1050]: [default-rtr] (ip4u): UPDATE from 10.0.3.5 with attributes:
RP/0/RP1/CPU0:Feb 28 18:10:31.461 : bgp[1050]: [default-rtr] (ip4u): nexthop 10.0.3.5/32, origin i
RP/0/RP1/CPU0:Feb 28 18:10:31.461 : bgp[1050]: [default-rtr] (ip4u): UPDATE from 10.0.3.5, prefix 12.0.0.0/24 (path ID: none) DENIED due to:
RP/0/RP1/CPU0:Feb 28 18:10:31.461 : bgp[1050]: [default-rtr] (ip4u): malformed update 'treat-as-withdraw';
RP/0/RP0/CPU0:Feb 28 18:10:31.462 : bgp[1050]: [default-rtr]: aspath first AS is 1537212616, not 200000
RP/0/RP0/CPU0:Feb 28 18:10:31.462 : bgp[1050]: [default-rtr]: Invalid ASPATH segment received from 10.0.3.5
RP/0/RP0/CPU0:Feb 28 18:10:31.462 : bgp[1050]: [default-rtr]: !!!!!!!!!!!!!:: ERROR_HANDLING<<10.0.3.5>> :: errfl=0x00000200, attrfl=0x40, attrcode=2, attrlen=6:: errhenabled=1, action=4:: MSG=0x7ffb84000cd8 (fl=0x00000200, finalaction=4, elemcount=1):: msglindex=1, msgcount=2307
RP/0/RP0/CPU0:Feb 28 18:10:31.462 : bgp[1050]: [default-rtr]: UPDATE from 10.0.3.5 contains nh 10.0.3.5/32, gw_afi 0, flags 0x20000, nlri_afi 0
RP/0/RP1/CPU0:Feb 28 18:10:31.461 : bgp[1050]: [default-rtr] (ip4u): UPDATE from 10.0.3.5, prefix 12.0.1.0/24 (path ID: none) DENIED due to:
RP/0/RP1/CPU0:Feb 28 18:10:31.461 : bgp[1050]: [default-rtr] (ip4u): malformed update 'treat-as-withdraw';
RP/0/RP1/CPU0:Feb 28 18:10:31.461 : bgp[1050]: [default-rtr] (ip4u): UPDATE from 10.0.3.5, prefix 12.0.2.0/24 (path ID: none) DENIED due to:
RP/0/RP1/CPU0:Feb 28 18:10:31.462 : bgp[1050]: [default-rtr] (ip4u): malformed update 'treat-as-withdraw';
RP/0/RP1/CPU0:Feb 28 18:10:31.462 : bgp[1050]: [default-rtr] (ip4u): UPDATE from 10.0.3.5, prefix 12.0.3.0/24 (path ID: none) DENIED due to:

The line in red I find particularly weird. The session does come up, but NCS5k does not accept incoming routes.

Any suggestions?

c.

[mivens]

What is the neighbour AS you have configured on the NCS-5500 and the Spirent?

If the first AS in the path doesn't match, it will be rejected unless you configure "enforce-first-as disable"

[Carlos A. Silva]

We tried the command and it didn't work.

The question is: why is the NCS getting that non-existent ASN in the aspath?

[smailmilak]

Hi Carlos,

we have the same issue on ASR9912 and 6.1.3.

Did you solve this issue and if yes, how?

[Carlos A. Silva]

Hi!

We didn't. We just used a router instead of the Spirent Traffic Generator and it worked.

Regards,

c.

[smailmilak]

We have solved it using this command under neighbor configuration.

"enforce-first-as disable"

[Carlos A. Silva]

Great to know, just in case. We were working with an NCS5508, though.

[xthuijs]

hi carlos,

this: aspath first AS is 1537212616, not 200000 means that the as path attribute for the prefix is not what was expected for the update.

this is not a bug per-se but may be a mis configuration somewhere, this if you have a router bgp <something> with a neighbor <spirent> remote-as 200000 configured on the device under test.

BGP between ncs5500/asr9k/xrv and any xr device operates the same, there is no platform dependency here.

cheers!

xander

[hfarias]

Hi do you have a solution for this?

i have the same problem :

Received unreachables from 172.16.2.20: attrcode=15, attrwdrflags=0x00000000
RP/0/RSP1/CPU0:Mar 13 01:01:19 : bgp[1067]: [default-rtr] (vpn4u): UPDATE from 172.16.2.20, prefix 2ASN:28114:28114:154.68.160.0/22 (path ID: none) withdrawn

[smailmilak]

Hi,

This is a eBGP session and you have a incoming route policy with PASS for this neighbor?

You should also check this out:

The BGP Enhanced Attribute Error Handling feature prevents peersessionsfrom flapping due to a malformed
Update. The malformed Update is treat-as-withdraw and does not cause the BGP session to be reset. This
feature is enabled by default, but can be disabled.
The features are implemented in the following order:
1 Received Updates that contain user-specified path attributes are treat-as-withdraw (as long as the NLRI
can be parsed successfully). If there is an existing prefix in the BGP routing table, it will be removed. The
neighbor path-attribute treat-as-withdraw command configures this feature.
2 User-specified path attributes are discarded from received Updates, and the rest of the Update is processed
normally. The neighbor path-attribute discard command configures this feature.
3 Received Updates that are malformed are treat-as-withdraw. This feature is enabled by default; it can be
disabled by configuring the no bgp enhanced-error command

[Carlos A. Silva]

Sadly, none of those commands are available on 6.1.3 on an NCS5500.  i know the router configuration is fine, if it's expected to be the same as in an ASR9000, for example. Spirent looks fine.

[Adam Vitkovsky]

Hmmm seems like the message was not parsed correctly, and it messed up the AS-PATH attribute, it thinks the first AS is 1537212616, not 200000 and probably the expected length is not matching up either triggering the Enhanced Attribute Error Handling.

Most likely a bug in the code, so you might want to open up a TAC case on this.

adam

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