PMTU_MaintainSeparate.seq - PMTU estimates for each destination address of its peer MUST maintain separate
To check the endpoint MUST maintain separate MTU estimates for each destination
address of its peer.
./PMTU_MaintainSeparate.seq [-tooloption ...] -pkt ./PMTU_MaintainSeparate.def
-tooloption : v6eval tool option
See Also: ../common/STD_PKT_COMMON.def
../common/SCTP_COMMON.def
Association not established between endpoint A and B. Also arrange the
data in endpoint B such that upper layers send associate primitive to
startup an association with endpoint A.
Endpoint A Endpoint B ULP
(ESTABLISHED) (ESTABLISHED)
<----- Send
<---------------- DATA
(IP=x)
ICMP ----------------->
(Packet Too Big)
<---------------- DATA (retransmission without fragment)
(IP=y)
Do Not Send SACK
<---------------- DATA (Fragment 1)
(IP=x)
<---------------- DATA (Fragment 2)
(IP=x)
SACK ----------------->
TEST DESCRIPTION:
1. Attempt to change PMTU of an association between endpoint A (IP=x) and
endpoint B by sending ICMP message.
2. ICMP message is sent with "Fragmentation Needed" or "Packet Too Big.
3. Check A: Data be retransmission be not fragmented on IP=y.
4. Check B: Data be retransmission be fragmented on IP=x.
None
RFC 4960
7.3. Path MTU Discovery
[RFC4821], [RFC1981], and [RFC1191] specify "Packetization Layer Path
MTU Discovery", whereby an endpoint maintains an estimate of the
maximum transmission unit (MTU) along a given Internet path and
refrains from sending packets along that path that exceed the MTU,
other than occasional attempts to probe for a change in the Path MTU
(PMTU). [RFC4821] is thorough in its discussion of the MTU discovery
mechanism and strategies for determining the current end-to-end MTU
setting as well as detecting changes in this value.
An endpoint SHOULD apply these techniques, and SHOULD do so on a
per-destination-address basis.
There are two important SCTP-specific points regarding Path MTU
discovery:
1) SCTP associations can span multiple addresses. An endpoint MUST
maintain separate MTU estimates for each destination address of
its peer.
2) The sender should track an association PMTU that will be the
smallest PMTU discovered for all of the peer's destination
addresses. When fragmenting messages into multiple parts this
association PMTU should be used to calculate the size of each
fragment. This will allow retransmissions to be seamlessly sent
to an alternate address without encountering IP fragmentation.