Cant Ping with packets with MTU larger than 1518 Bytes
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Posted by wilowolf on May 24, 2009, 12:32 am
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I have two routers connected connected back to back with an Ethernet cable. I set MTU size on bother GigaEthernet intefaces to 1524 yet, when the routers cant ping each with packets of size more than 1518 when set the DF on. Any hint ? | ||||||||||
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Posted by bod43 on May 24, 2009, 7:01 am
Please log in for more thread options Maybe you have already taken this into account, however: There is no standard for a ping program. The size specified as a parameter to the ping command may not be the "ethernet" packet length. It may be - Frame length with CRC - default for ethernet is 1518 Frame length without the CRC - 1514 IP packet total length - 1500 IP packet total length less the IP header ICMP payload length - ? Some other number the designer fancied at the time It may also vary (and does if I recall correctly) with the exact ping program being used. Cisco router one being different from Windows one I suspect. I always just check with wireshark on a PC. I seem to recall that on Windows you specify -l 1472 to get a maximal length ethernet packet (however that may well be incorrect). This I guess will be the ICMP payload length. | ||||||||||
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Posted by Aaron Leonard on May 26, 2009, 6:28 pm
Please log in for more thread options ~ I have two routers connected connected back to back with an Ethernet
~ cable. I set MTU size on bother GigaEthernet intefaces to 1524 yet, ~ when the routers cant ping each with packets of size more than 1518 ~ when set the DF on. Any hint ? Both mtu and ip mtu are boosted, yes? | ||||||||||
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>
> I have two routers connected connected back to back with an Ethernet
> cable. I set MTU size on bother GigaEthernet intefaces to 1524 yet,
> when the routers cant ping each with packets of size more than 1518
> when set the DF on. Any hint ?