[c-nsp] GRE fragmentation and ASR9001

Adam Vitkovsky Adam.Vitkovsky at gamma.co.uk
Tue Aug 11 05:43:47 EDT 2015

Hi Gert,

There are counters suggesting that IPv4 frames are punted to LC CPU to be fragmented.

sh controllers np descriptions location 0/x/cpu0

RSV_PUNT_IP_MTU_EXCEEDED                                  L3       Egress IP packets that exceed the interface MTU.  IPv4 frames are punted to LC CPU to be fragmented. IPv6 frames are punted to LC CPU be dropped and generate ICMP response.Punt rate limit is very low to protect LC CPU

IPV4_FRAG_NEEDED_PUNT                                     Punt     IP MTU Exceeded. Punted to CPU for fragmentation

MPLS_FRAG_NEEDED_PUNT                                     Punt     MPLS packet for which fragmentation is required

IPV4_FRAG_TUNNEL                                          Punt     Not implemented by ucode
-this one actually concerns me
-does it mean it's going to be slow, or punted to RP, or just dropped
-not sure what I should make up from this


        Adam Vitkovsky
        IP Engineer

T:      0333 006 5936
E:      Adam.Vitkovsky at gamma.co.uk
W:      www.gamma.co.uk

This is an email from Gamma Telecom Ltd, trading as “Gamma”. The contents of this email are confidential to the ordinary user of the email address to which it was addressed. This email is not intended to create any legal relationship. No one else may place any reliance upon it, or copy or forward all or any of it in any form (unless otherwise notified). If you receive this email in error, please accept our apologies, we would be obliged if you would telephone our postmaster on +44 (0) 808 178 9652 or email postmaster at gamma.co.uk

Gamma Telecom Limited, a company incorporated in England and Wales, with limited liability, with registered number 04340834, and whose registered office is at 5 Fleet Place London EC4M 7RD and whose principal place of business is at Kings House, Kings Road West, Newbury, Berkshire, RG14 5BY.

-----Original Message-----
> From: cisco-nsp [mailto:cisco-nsp-bounces at puck.nether.net] On Behalf Of
> Gert Doering
> Sent: 11 August 2015 09:53
> To: cisco-nsp at puck.nether.net
> Subject: [c-nsp] GRE fragmentation and ASR9001
> Hi,
> my google fu is failing me - so apologies if this is in easily findable
> documentation...
> I want (need) to connect two ASR9001s over a GRE tunnel "across the
> public Internet" (= outside MTU 1500), but need to provide a larger inner
> MTU (~1600).  So, fragmentation and reassembly required.
> Easy question: can the ASR9001 do that (in hardware, obviously)?
> Pointers to documentation appreciated :-)
> (Current XR release is 4.3.4, but knowing that "it is supported starting
> in 5.17.4" would also be useful information)
> gert
> --
> USENET is *not* the non-clickable part of WWW!
>                                                            //www.muc.de/~gert/
> Gert Doering - Munich, Germany                             gert at greenie.muc.de
> fax: +49-89-35655025                        gert at net.informatik.tu-muenchen.de

More information about the cisco-nsp mailing list