[j-nsp] Command to modify ADSPEC object default on PATH messages.

[Nalkhande Tarique Abbas]

AFAIK, JUNOS uses the Adspec field for maximum transmission unit (MTU)
negotiation.

So when an LSP is created across a set of links with different MTU
sizes, the ingress router does not know what the smallest MTU is on the
LSP path. By default, the maximum packet size for the LSP is based on
the MTU for the outgoing interface for the LSP on the ingress router.

If this MTU is larger than the MTU of one of the intermediate links,
traffic might be dropped, because MPLS packets cannot be fragmented. 

To prevent this type of packet loss in MPLS LSPs, you can configure MTU
signaling in RSVP. Juniper supports the Integrated Services object for
MTU signaling in RSVP. 

MTU signaling in RSVP is disabled by default.
To configure maximum transmission unit (MTU) signaling in RSVP, you need
to configure MPLS to allow IP packets to be fragmented before they are
encapsulated in MPLS. You also need to configure MTU signaling in RSVP. 
To configure MTU signaling in RSVP, include the path-mtu statement:

path-mtu { 
allow-fragmentation; 
rsvp { 
mtu-signaling;  <<--
} 
}

lab at ntarique# run show mpls lsp transit detail 
Transit LSP: 1 sessions

192.168.255.1
  From: 192.168.255.7, LSPstate: Up, ActiveRoute: 1

... truncated...

  FastReroute desired
  PATH rcvfrom: 192.168.245.46 (so-0/2/1.0) 42 pkts
  Adspec: received MTU 1500 sent MTU 1500  <<<---
 


Thanks & Regards,
Tarique A. Nalkhande

-----Original Message-----
From: juniper-nsp-bounces at puck.nether.net
[mailto:juniper-nsp-bounces at puck.nether.net] On Behalf Of Thiago
Drechsel
Sent: Friday, August 07, 2009 6:37 PM
To: Juniper List
Subject: [j-nsp] Command to modify ADSPEC object default on PATH
messages.

Hi list.

Does anybody know what is the configuration needed to add "Guaranteed
Service" parameters, on ADSPEC object (RSVP PATH messages)?

By default, I see that JUNOS only sends "Default General Parameters" and
"Controlled Load" within PATH....

Thank you!

-- 
Thiago Drechsel


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