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[Junos] Understanding transit MPLS packet with ethernet, mpls and IP header details

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Article ID: KB33472 KB Last Updated: 29 Mar 2019Version: 1.0
Summary:

This article provides an example transit MPLS packet to explain the details of the Ethernet header, MPLS header, and IP where IP is a payload.

Solution:

The following is a sample packet/parcel with14 byte Ethernet header and Ethertype 0x8847, which denotes MPLS unicast and with IP payload.

ETHERNET MPLS IPV4
0  1  2  3  4  5  6  7  8  9 10 11 12 13 14 15
AC 4B C8 45 80 A4 9C CC 83 09 41 00 88 47 49 4D
01 40 45 00 04 04 61 46 00 00 40 01 E3 A9 98 01
02 01 98 00 00 07 08 00 B7 32 B0 A2 00 2C 5B F9
E6 E8 00 07 C9 20 BA DC 0F FE BA DC 0F FE BA DC
0F FE BA DC 0F FE BA DC 0F FE BA DC 0F FE BA DC
0F FE BA DC 0F FE BA DC 0F FE BA DC 0F FE BA DC
0F FE BA DC 0F FE BA DC 0F FE BA DC 0F FE BA DC
0F FE BA DC 0F FE BA DC 0F FE BA DC 0F FE BA DC
0F FE BA DC 0F FE BA DC 0F FE BA DC 0F FE BA DC
0F FE BA DC 0F FE BA DC 0F FE BA DC 0F FE BA DC
0F FE BA DC 0F FE BA DC 0F FE BA DC 0F FE BA DC
0F FE BA DC 0F FE BA DC 0F FE BA DC 0F FE BA DC
0F FE BA DC 0F FE BA DC 0F FE BA DC 0F FE BA DC
0F FE BA DC 0F FE BA DC 0F FE BA DC 0F FE BA DC
0F FE BA DC 0F FE BA DC 0F FE BA DC 0F FE BA DC
0F FE BA DC 0F FE BA DC 0F FE BA DC 0F FE

This sample packet shows the details of the Ethernet header, MPLS header, and IP.

This is for reference when troubleshooting similar packet types. Below are the details of each header type.

Ethernet frame - 14Byte header + 4Byte trailer
 0  1  2  3  4  5  6  7  8  9 10 11 12 13 
AC 4B C8 45 80 A4 9C CC 83 09 41 00 88 47

Dest mac address   - AC 4B C8 45 80 A4
Source mac address - 9C CC 83 09 41 00 
Type – 0x8847 <-- various types here.

MPLS header - 4bytes (First 20bytes is the label value)

 0  1  2  3
49 4D 01 40

Label–0x494D0 = 300240
EXP&S-0x1(0001)-Exp=000,Bottom of label Stack-1
TTL- 0x40(0100 0000) = 64

IP Payload - 20bytes

 0  1  2  3  4  5  6  7  8  9 10 11 12 13 14 15 16 17 18 19
45 00 04 04 61 46 00 00 40 01 E3 A9 98 01 02 01 98 00 00 07 

Ver–4,Header length-5(20b),DSCP&ECN -000, 
Total length 0404 (1028b), Identification – 6146(24902), 
Flags 00 00 (Reserved–0,DF-0, MF-0,Fragmentoffset-0),TTL- 40 (64),
Protocol-ICMP 01 (1),Header checksum-E3 A9,
Source IP – 98 01 02 01(152.1.2.1), Dest IP-98 00 00 07(152.0.0.7)
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