On Wed, 7 Dec 2011, Peter Rathlev wrote:
If the L2TPv2 packets cannot exceed 1500 bytes then the ICMP payload
size of an encapsulated packet cannot exceed 1430 bytes, assuming you're
not transporting a 802.1Q frame.
An ICMP packet with 1430 bytes payload, 8 bytes ICMP header and 20 bytes
IP header is 1458 bytes. Next comes the Ethernet frame header of 14
bytes. Add to this the 8 bytes L2TPv3 header and 20 bytes outer IP
header and you're at the 1500 bytes.
Removing PMTUD and via DF-bit allowing fragmetation greatly increases
the CPU load on the devices terminating the tunnels.
Understood. What I don't understand is why the large pings (in this case
large is anything > 1430) will sometimes work and sometimes not. There is
no packet loss between the two routers and pmtud works between them. They
can ping each other with large packets all day. Not so the xconnected
hosts.
Antonio Querubin
e-mail: [email protected]
xmpp: [email protected]
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