[c-nsp] Fwd: IPV6 Path MTU DIscovery Test
Xu Hu
jstuxuhu0816 at gmail.com
Wed Aug 1 10:26:20 EDT 2012
Wow, good idea, i heard the tracepath6 first time, just checked, maybe i
can use this command.
What exactly i want to test is how the PMTUD works, because i don't have
host int the test scenario, just have the router, so need to simulate the
traffic from router, but my first thought is using the ping traffic, so
let's say if i change the MTU in the path to a low one, the ping traffic
will be dropped, the ping traffic cannot change the mtu automatically,
because i already define the traffic size in the ping packet.
The tracepath6 command as below, first line can show the pmtu.
tracepath6 www.ripe.net -n
1?: [LOCALHOST] pmtu 1500
1: 2001:db1::3 1.785ms
2: 2001:db1::2 asymm 1 1.944ms
3: 2001:db1:2:16::9 asymm 2 2.937ms
4: ::ffff:154.0.0.13 asymm 11 16.193ms
5: ::ffff:154.0.0.46 asymm 11 16. 60ms
6: ::ffff:154.0.0.9 asymm 11 16. 69ms
7: ::ffff:154.0.0.134 asymm 11 16.279ms
8: 2001:550:3::8a asymm 9 15.860ms
9: 2001:5a0:600:500::a asymm 8 16.746ms
10: 2001:5a0:f00:400::1 19.212ms
11: 2001:5a0:2000:400::19 asymm 9 90.538ms
12: 2001:5a0:2000:500::1 asymm 8 86.440ms
13: 2001:5a0:2000:500::a asymm 9 103.741ms
14: 2001:5a0:200:100::5 asymm 11 103.324ms
15: 2001:5a0:200:200::16 asymm 9 97.851ms
16: no reply
17: 2001:67c:2e8:27::1 asymm 13 98.410ms !A
Resume: pmtu 1500
2012/8/1 Chris Conn <CConn at b2b2c.com>
> Why not just use tracepath6? What exactly do you want to test? That
> PMTUD is broken or not?
>
> -----Original Message-----
> From: cisco-nsp-bounces at puck.nether.net [mailto:
> cisco-nsp-bounces at puck.nether.net] On Behalf Of Xu Hu
> Sent: 1 août 2012 09:54
> To: Oliver Boehmer (oboehmer)
> Cc: cisco-nsp at puck.nether.net
> Subject: Re: [c-nsp] Fwd: IPV6 Path MTU DIscovery Test
>
> 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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> > > >
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