Tech Stuff, WorkMaximum MTU Discovery

Maximum MTU Discovery

Learnt this neat little trick to discover MTU on a link:

pe1.zzz1#ping
Protocol [ip]:
Target IP address: 10.92.249.166
Repeat count [5]: 1
Datagram size [100]:
Timeout in seconds [2]:
Extended commands [n]: y
Source address or interface:
Type of service [0]:
Set DF bit in IP header? [no]: y
Validate reply data? [no]:
Data pattern [0xABCD]:
Loose, Strict, Record, Timestamp, Verbose[none]: ver
Loose, Strict, Record, Timestamp, Verbose[V]:
Sweep range of sizes [n]: y
Sweep min size [36]: 1500
Sweep max size [18024]: 2000
Sweep interval [1]:
Type escape sequence to abort.
Sending 501, [1500..2000]-byte ICMP Echos to 10.92.249.166, timeout is 2 seconds:
Packet sent with the DF bit set
Reply to request 0 (28 ms) (size 1500)
Reply to request 1 (28 ms) (size 1501)
Reply to request 2 (24 ms) (size 1502)
Reply to request 3 (28 ms) (size 1503)
Reply to request 4 (24 ms) (size 1504)
Reply to request 5 (28 ms) (size 1505)
Reply to request 6 (24 ms) (size 1506)
Reply to request 7 (28 ms) (size 1507)
Reply to request 8 (24 ms) (size 1508)
Reply to request 9 (28 ms) (size 1509)
Reply to request 10 (24 ms) (size 1510)
Reply to request 11 (24 ms) (size 1511)
Reply to request 12 (28 ms) (size 1512)
Request 13 timed out (size 1513)
Request 14 timed out (size 1514)
Request 15 timed out (size 1515)
Success rate is 76 percent (13/17), round-trip min/avg/max = 24/26/28 ms
pe1.zzz1#

We can conclude the maximum MTU is 1512!

Very neat way to quickly discover MTU!

Categories: Tech Stuff, Work