Caching learned MSS/MTU values

[Tassos Chatzithomaoglou]

I see that WinXP keeps the /128 for the last 32 entries.

C:\Documents and Settings\Tassos>ipv6 rc
2a02:1788:4fd::b2ff:5201 via 4/fe80::218:18ff:fef6:5b54
     src 4/2a02:2148:82:6000:1430:f026:c55a:b75b
     PMTU 1500
2a02:1788:2fd::ab via 4/fe80::218:18ff:fef6:5b54
     src 4/2a02:2148:82:6000:1430:f026:c55a:b75b
     PMTU 1500
2a02:2148:2fff:ff02::3e01:2619 via 4/fe80::218:18ff:fef6:5b54
     src 4/2a02:2148:82:6000:1430:f026:c55a:b75b
     PMTU 1500


C:\Documents and Settings\Tassos>netsh interface ipv6 show global
Querying active state...

General Global Parameters
---------------------------------------------
Default Hop Limit                   : 128 hops
Neighbor Cache Limit                : 256 entries per interface
Route Cache Limit                   : 32 entries
Reassembly Limit                    : 16770400 bytes


Win7 seems to keep /128 for the last 128 entries.

C:\Users\Tassos>netsh interface ipv6 show destinationcache

Interface 10: Local Area Connection


PMTU Destination Address                           Next Hop Address
---- --------------------------------------------- -------------------------
1492 2001:0:5ef5:79fb:1c3e:d863:c447:6318          fe80::200:ff:fe00:0
1492 2001:0:9d38:6ab8:4a3:31f0:411e:6346           fe80::200:ff:fe00:0
1492 2001:0:9d38:6ab8:10c5:11cb:b08a:5623          fe80::200:ff:fe00:0
1492 2001:0:9d38:6ab8:3485:2015:a1ca:a777          fe80::200:ff:fe00:0
1492 2001:0:9d38:6abd:1cbd:1b0c:e0f1:34d3          fe80::200:ff:fe00:0
1492 2001:0:9d38:90d7:20a2:147a:9a93:4e6b          fe80::200:ff:fe00:0
1500 2a02:2149:8104:3100:4484:bf55:88d6:bcc3       2a02:2149:8104:3100:4484:bf55:88d6:bcc
1492 fe80::200:ff:fe00:0                           fe80::200:ff:fe00:0
1492 2001:0:9d38:90d7:2020:3f27:a9ec:39ce          fe80::200:ff:fe00:0
1492 2001:0:5ef5:79fd:873:3f92:ac11:1ee6           fe80::200:ff:fe00:0

C:\Users\Tassos>netsh interface ipv6 show global
Querying active state...

General Global Parameters
---------------------------------------------
Default Hop Limit                   : 128 hops
Neighbor Cache Limit                : 256 entries per interface
Route Cache Limit                   : 128 entries per compartment


--
Tassos

Jason Fesler wrote on 17/10/2013 19:05:
> I'm once again considering trying to improve on the test-ipv6.com <http://test-ipv6.com> PMTUD failure detection. Due to limitations on the client side I can't use raw sockets to generate test packets. The client is JavaScript and runs in a browser; all I can do is try fetching urls from multiple locations, each with a different MTU. 
>
> I know that the various operating systems tend to cache any PMTUD issues that they can detect; future connections to that destination will use smaller packets accordingly. What I can not see to find is an adequate description of what granularity this gets cached with. /128? /64?   Also, I the absence of Packet Too Big messages, what does each OS do?
>
> If anyone has pointers, please share. It will affect what and how I can improve the site, given the restrictions I have with the client side.
>
>
>
>
> -- 
>  Jason Fesler, email/jabber <jfesler at gigo.com <mailto:jfesler at gigo.com>> resume: http://jfesler.com
>  "Give a man fire, and he'll be warm for a day;
>  set a man on fire, and he'll be warm for the rest of his life."
>
>

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