Subject: IP Source Route Option

From: [email-masked]
Date: Thu, 26 Apr 2001 16:20:06 +0530

Hi All,

I have a small doubt. Let an unlabelled IP packet with IP source route option
enabled comes in MPLS domain. Let the packet is assigned to a LSP (say numbered
1). While traversing the MPLS domain, packet will not go to the Network layer,
thus the LSR in between the ingress LSR and egress LSR cannot insert their IP
addresses in the datagram. So does MPLS supports IP source route option or it
does not support it?

Thanks
Mohit Goel

---

From: [email-masked]
Date: Thu, 26 Apr 2001 16:23:23 +0530

hi mohit!
     Ideally this thing should be handled at the Ingress LER and he should
translate the IP Source Route to MPLS sourse Route by defining a complete path
for the packet (means asking the downstream routers for this). The question
still hold weight as to what should be done if such a path does not exist at the
time of the packet coming in or the path cannot be setup even when requested. My
guess is that its best in both cases to discard the packet and send a normal
ICMP packet back to source as is normally done.  Going a bit deeper we generally
use IP Source Routing for testing purposes and not as a means of data path
reservation. Hence it might make sense to try and set up the LSP requested
starting at the Ingress LER to the Egress LER if possible while holding on to
the packet. This does complicate things but I guess if we have to do source
routing we have to do this. ;o(
regards
sumit

[email-masked] on 04/26/2001 04:20:06 PM

To:   [email-masked]
cc:    (bcc: Sumit Chauhan/HSS)

Subject:  IP Source Route Option

Hi All,

Thanks
Mohit Goel

---

From: [email-masked]
Date: Thu, 26 Apr 2001 16:54:42 +0530

Hi Sumit !

But how mpls will handle the IP's Record route option which requires that each
intermediate router should insert its IP address in the datagram. MPLS cannot
drop that packet simply because record route option is enabled in it. Moreover
if explicit routing is there then ingress router can insert the complete IP
addresses of the intermediate LSRs in the datagram, but what will happen in the
case of hop by hop LSP.

Thanks
Mohit Goel

[email-masked] on 04/26/2001 04:23:23 PM

To:   Mohit Goel/HSS@HSS
cc:   [email-masked]

Subject:  Re: IP Source Route Option

hi mohit!

To:   [email-masked]

Hi All,

Thanks
Mohit Goel

---

From: "Peter Ashwood-Smith" <[email-masked]>
Date: Fri, 27 Apr 2001 22:29:07 -0400

I assume it would be placed on the appropriate LSP as normal. Then, when it
popped off the LSP it would route again, as usual. So, if the source route
were not carefully structured to take the LSP into account it could take you
all the way back to say the second router along the LSP, which would then
put you on possibly the same LSP. You would then pop off the end of the LSP
and be returned by normal routing to possibly the third router along the LSP
... kind of neat but undesirable behaviour.

Anyway, source routing and MPLS LSP's are somewhat orthogonal but source
routing would I presume work if you did not specify any of the routers along
which the LSP already flowed in the source route, otherwise it would loop
around a bit before getting to its destination.

Cheers,

Peter Ashwood-Smith

	-----Original Message-----
	From:	[email-masked] [SMTP:[email-masked]]
	Sent:	Thursday, April 26, 2001 6:50 AM
	To:	[email-masked]
	Subject:	IP Source Route Option

	Hi All,

	I have a small doubt. Let an unlabelled IP packet with IP source
route option
	enabled comes in MPLS domain. Let the packet is assigned to a LSP
(say numbered
	1). While traversing the MPLS domain, packet will not go to the
Network layer,
	thus the LSR in between the ingress LSR and egress LSR cannot insert
their IP
	addresses in the datagram. So does MPLS supports IP source route
option or it
	does not support it?

	Thanks
	Mohit Goel