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OCI: Tcpdump Shows Packet Size Greater than the MTU on NIC (Doc ID 2526147.1)

Last updated on OCTOBER 07, 2020

Applies to:

Oracle Cloud Infrastructure - Version N/A and later
Linux x86-64 on Oracle Public Cloud

Symptoms

In tcpdump, you see the packets length are greater than MTU 1500

# ifconfig eno2
eno2: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 1500
inet xxx.xxx.xxx.xxx(eno2 IP addr) netmask x.x.x.x broadcast x.x.x.x
ether <MAC ADDR> txqueuelen 1000 (Ethernet)
RX packets 11551418 bytes 5210005048 (4.8 GiB)
RX errors 0 dropped 0 overruns 0 frame 2
TX packets 19540560 bytes 76710287934 (71.4 GiB)
TX errors 0 dropped 0 overruns 0 carrier 0 collisions 0

 # tcpdump -nni eno2 greater 1500 -c 10
tcpdump: verbose output suppressed, use -v or -vv for full protocol decode
listening on eno2, link-type EN10MB (Ethernet), capture size 262144 bytes
02:33:37.768716 IP xxx.xxx.xxx.xxx(eno2 IP addr).42373 > yyy.yyy.yyy.yyy.3260: Flags [.], seq 2243738059:2243740955, ack 3160073807, win 52886, options [nop,nop,TS val 1636514624 ecr 685734230], length 2896
02:33:37.768726 IP xxx.xxx.xxx.xxx(eno2 IP addr).42373 > yyy.yyy.yyy.yyy.3260: Flags [P.], seq 2896:8192, ack 1, win 52886, options [nop,nop,TS val 1636514624 ecr 685734230], length 5296
02:33:37.769608 IP xxx.xxx.xxx.xxx(eno2 IP addr).42373 > yyy.yyy.yyy.yyy.3260: Flags [.], seq 8192:12536, ack 1, win 52886, options [nop,nop,TS val 1636514625 ecr 685734230], length 4344
02:33:37.770157 IP xxx.xxx.xxx.xxx(eno2 IP addr).42373 > yyy.yyy.yyy.yyy.3260: Flags [P.], seq 12536:20576, ack 1, win 52886, options [nop,nop,TS val 1636514625 ecr 685739443], length 8040
02:33:37.770222 IP xxx.xxx.xxx.xxx(eno2 IP addr).42373 > yyy.yyy.yyy.yyy.3260: Flags [.], seq 20624:23520, ack 49, win 52886, options [nop,nop,TS val 1636514625 ecr 685739443], length 2896
02:33:37.770248 IP xxx.xxx.xxx.xxx(eno2 IP addr).42373 > yyy.yyy.yyy.yyy.3260: Flags [.], seq 23520:40896, ack 49, win 52886, options [nop,nop,TS val 1636514625 ecr 685739444], length 17376
02:33:37.770265 IP xxx.xxx.xxx.xxx(eno2 IP addr).42373 > yyy.yyy.yyy.yyy.3260: Flags [.], seq 40896:53928, ack 49, win 52886, options [nop,nop,TS val 1636514625 ecr 685739444], length 13032
02:33:37.770750 IP xxx.xxx.xxx.xxx(eno2 IP addr).42373 > yyy.yyy.yyy.yyy.3260: Flags [P.], seq 53928:57680, ack 97, win 52886, options [nop,nop,TS val 1636514626 ecr 685739444], length 3752
02:33:37.770992 IP xxx.xxx.xxx.xxx(eno2 IP addr).42373 > yyy.yyy.yyy.yyy.3260: Flags [P.], seq 57680:61824, ack 97, win 52886, options [nop,nop,TS val 1636514626 ecr 685739444], length 4144
02:33:37.771036 IP xxx.xxx.xxx.xxx(eno2 IP addr).42373 > yyy.yyy.yyy.yyy.3260: Flags [.], seq 52480:53928, ack 145, win 52886, options [nop,nop,TS val 1636514626 ecr 685739444], length 1448
10 packets captured
12 packets received by filter
0 packets dropped by kernel

Cause

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In this Document
Symptoms
Cause
Solution

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