ISIS 3 way handshake

[Ratheesh mv]

What is the difference between  "isis three-way-handshake ietf" and "isis three-way-handshake cisco" ?

When I did packet capture with isis three-way-handshake ietf there were extended local circuit ID , Neighbor system-ID  and neighbor extended local circuit ID fields in the TLV 240 but these fields were not present with isis three-way-handshake cisco.

Can someone explain the difference between those? 

Thanks in advance 

[balaji.bandi]

check this information may helop you :

try command - isis three-way-handshake ietf

https://www.ciscopress.com/articles/article.asp?p=26850&seqNum=5

[Harold Ritter · Accepted solution]

Hi @Ratheesh mv ,

"isis three-way-handshake ietf" enables the behavior describes in RFC5303.

"isis three-way-handshake cisco" is the default behavior and enables the pre RFC5303 behavior.

Please refer to RFC55303 for more information.

https://datatracker.ietf.org/doc/html/rfc5303

Regards,

[Ratheesh mv]

Hi Harold Ritter

I have understood working of RFC 5303.

Can you briefly explain about pre RFC5303 behaviour in your words ? It will be appreciated.

[Giuseppe Larosa · Accepted solution]

Hello @Ratheesh mv ,

pre RFC 5303 behaviuor is described in RFC Abstract:

>>

The IS-IS routing protocol (Intermediate System to Intermediate
   System, ISO 10589) requires reliable protocols at the link layer for
   point-to-point links.  As a result, it does not use a three-way
   handshake when establishing adjacencies on point-to-point media.
   This paper defines a backward-compatible extension to the protocol
   that provides for a three-way handshake.  It is fully interoperable
   with systems that do not support the extension.

   Additionally, the extension allows the robust operation of more than
   256 point-to-point links on a single router.

So pre RFC5303 implementations have the following limitations:

no three way handshake is actually performed on point to point links by IS-IS itself

Note: Cisco may have had a 3 way handshake using standard circuit IDs.

The second important limitation is the original circuit descriptors allowed to describe up to 256 different p2p links ( a single octet was used to describe the circuit ID)  on  a single router and this limit is too low for modern routers that can have thousands of logical interfaces and hundreds of physical interfaces.

Your wireshark packet captures confirm the use of extended circuit IDs descriptors when using ietf option.

>> When I did packet capture with isis three-way-handshake ietf there were extended local circuit ID , Neighbor system-ID and neighbor extended local circuit ID fields in the TLV 240 but these fields were not present with isis three-way-handshake cisco.

Hope to help

Giuseppe