Subject: Re: MPLS and fragmentation..

From: "Faisal S. Naik" <[email-masked]>
Date: Tue, 5 Dec 2000 00:08:15 +0500

hello soumen,
Isnt this Ip fragmentation a part of the router before the packet enters the
MPLS domain. Within the domain, there is only the label swapping mechanism
that is working, with nothing to mention about the fragmentation part.
Esp in cases of IPv6 fragmentation is not at all allowed, for exceptional
cases, extended headers of IPv6 are used.
Am i right Nisar saheb :)
Regards,
Faisal Naik

---

From: [email-masked]
Date: Mon, 4 Dec 2000 16:49:01 -0500

>"Wilder, David" wrote:
>>
>> This is true; IP fragmentation is done by IP before entering the MPLS
>> domain.  However,  there are case where adding the 4 byte label is
>> going to cause the packet to now exceed the max mtu size.  Then  one
>> must look at how to handle that situation i.e. fragment, discard or do
>> nothing.
>
>I don't see what the problem is here.  If the ingress router knows the
>MTU for the entire path (as it must, if it is going to fragment
>packets), then it should not be a big deal to subtract a constant value
>from the computed MTU (to accomodate the label header) and fragment to
>that value instead.
>

In the case of an LSP setup using CR-LDP, how does the ingress router
determine the MTU for the path? (assuming the ingress router is not also
a host utilizing the LSP)