[c-nsp] Fwd: IPV6 Path MTU DIscovery Test

[Xu Hu]

Must use the TCP packets? I want to just use the ping packet to test the
effect of PMTUD. Is any simple way to test this feature?

Another thing, if use the iBGP to test, i find one show ip bgp neighbor
command as below, the MSS you mentioned is the "*Datagrams (max data
segment is 1460 bytes):*" ?

Thanks for your help.
Hu Xu

Router# *show ip bgp neighbors 172.16.232.178*


BGP neighbor is 172.16.232.178,  remote AS 10, external link

 Index 1, Offset 0, Mask 0x2

  Inbound soft reconfiguration allowed

  BGP version 4, remote router ID 172.16.232.178

  BGP state = Established, table version = 27, up for 00:06:12

  Last read 00:00:12, hold time is 180, keepalive interval is 60 seconds

  Minimum time between advertisement runs is 30 seconds

  Received 19 messages, 0 notifications, 0 in queue

  Sent 17 messages, 0 notifications, 0 in queue

  Inbound path policy configured

  Route map for incoming advertisements is testing

  Connections established 2; dropped 1

Connection state is ESTAB, I/O status: 1, unread input bytes: 0

Local host: 172.16.232.181, Local port: 11002

Foreign host: 172.16.232.178, Foreign port: 179


Enqueued packets for retransmit: 0, input: 0, saved: 0


Event Timers (current time is 0x530C294):

Timer          Starts    Wakeups            Next

Retrans            12          0             0x0

TimeWait            0          0             0x0

AckHold            12         10             0x0

SendWnd             0          0             0x0

KeepAlive           0          0             0x0

GiveUp              0          0             0x0

PmtuAger            0          0             0x0


iss:  133981889  snduna:  133982166  sndnxt:  133982166     sndwnd:  16108

irs: 3317025518  rcvnxt: 3317025810  rcvwnd:      16093  delrcvwnd:    291


SRTT: 441 ms, RTTO: 2784 ms, RTV: 951 ms, KRTT: 0 ms

minRTT: 0 ms, maxRTT: 300 ms, ACK hold: 300 ms

Flags: higher precedence, nagle


*Datagrams (max data segment is 1460 bytes):*

Rcvd: 15 (out of order: 0), with data: 12, total data bytes: 291

Sent: 23 (retransmit: 0), with data: 11, total data bytes: 276


2012/8/1 Oliver Boehmer (oboehmer) <oboehmer at cisco.com>

> Well, you need to create TCP connections to see the effect of PMTUD.. you
> could build an iBGP session across the test network, and play around with
> the minimum link MTU along the path. The MSS (shown in show bgp neighbor
> ..) should adapt as you change it..
>
>         oli
>
> > -----Original Message-----
> > From: cisco-nsp-bounces at puck.nether.net [mailto:cisco-nsp-
> > bounces at puck.nether.net] On Behalf Of Xu Hu
> > Sent: 01 August 2012 02:33
> > To: cisco-nsp at puck.nether.net
> > Subject: [c-nsp] Fwd: IPV6 Path MTU DIscovery Test
> >
> > Anybody have any good idea?
> >
> > Thanks advance for any inputs,
> > Xu Hu
> >
> > Begin forwarded message:
> >
> > > From: TJ <trejrco at gmail.com>
> > > Date: 1 August, 2012 5:23:46 GMT+08:00
> > > To: Xu Hu <jstuxuhu0816 at gmail.com>
> > > Subject: Re: [c-nsp] IPV6 Path MTU DIscovery Test
> > > Reply-To: trejrco at gmail.com
> > >
> > > In order to test it, take one of the links along the path and change
> the
> > (IPv6) MTU to something smaller - say 1300B.  Then send large packets,
> with
> > WireShark running.  And no, you cannot disable PMTUD in IPv6.
> > >
> > > HTH!
> > > /TJ
> > >
> > >
> > > On Tue, Jul 31, 2012 at 6:43 AM, Xu Hu <jstuxuhu0816 at gmail.com> wrote:
> > > Hi Experts,
> > >
> > > I have some queries about the PMTU for IPv6.
> > > 1. From my understanding, path MTU discovery in IPv6 allows a host to
> > > dynamically discover and adjust to differences in the MTU size of every
> > > link along a given data path, So the fragmentation is handled by the
> > > source, if i want to test this feature in the IPv6 network, anyone have
> > any
> > > good ideas?
> > > For example, as below topology, if i want to test the Path MTU
> discovery,
> > > how to test, i can ping from CE-1  to CE--2 with a specific IPv6 packet
> > > size.
> > > CE-1------PE-1------------PE-2--------CE-2
> > >
> > > 2. If i need to configure the Path MTU discovery, just one command
> > > mentioned in Cisco.com, which is "ipv6 flowset" under configuration
> mode.
> > > So if i want to disable that in test scenario, just using the "no ipv6
> > > flowset" is okay? Cisco don't mentioned that.
> > > By default, it is enable for ip routers or not?
> > >
> > > Thanks for any inputs.
> > >
> > > Best Regards,
> > > Hu Xu
> > > _______________________________________________
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