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Masood Ahmad Shah

This blog contains a summary of my research readings and thoughts in system and network engineering. View Masood Shah's profile on LinkedIn

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Configuring the Juniper Media, IP & MPLS MTU

Here I have some information on MTU Juniper, I had investigated it for a customer while ago. The actual frames transmitted also contain cyclic redundancy check (CRC) bits, which are not part of the media MTU. For example, the media MTU for a Gigabit Ethernet interface is specified as 1500 bytes, but the largest possible frame size is actually 1504 bytes; you need to consider the extra bits in calculations of MTUs for interoperability.

 

                                                     Encapsulation Overhead by Encapsulation Type

 
Interface Encapsulation
Encapsulation Overhead (Bytes)

802.1Q/Ethernet 802.3

21

802.1Q/Ethernet Subnetwork Access Protocol (SNAP)

26

802.1Q/Ethernet version 2

18

ATM Cell Relay

4

ATM permanent virtual connection (PVC)

12

Cisco HDLC

4

Ethernet 802.3

17

Ethernet circuit cross-connect (CCC) and virtual private LAN service (VPLS)

4

Ethernet over ATM

32

Ethernet SNAP

22

Ethernet translational cross-connect (TCC)

18

Ethernet version 2

14

Extended virtual local area network (VLAN) CCC and VPLS

4

Extended VLAN TCC

22

Frame Relay

4

PPP

4

VLAN CCC

4

VLAN VPLS

4

VLAN TCC

22


Default media MTU = Default IP MTU + L2 encapsulation overhead
Default IP MTU = Default media MTU -  L2 encapsulation overhead
MPLS MTU = physical interface MTU - L2 encapsulation overhead - 12
If IP MTU is already set, so MPLS MTU = IP MTU + 20 bytes
IP MTU - payload without header!
 
Note: In other words, the formula used to determine the MPLS MTU is the following:
MPLS MTU = physical interface MTU - encapsulation overhead - 12

Published Tuesday, May 05, 2009 1:08 PM by jahil

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# MTU difference between Cisco and Juniper | Irfan Salam @ Thursday, December 19, 2013 7:25 PM

PingBack from http://irfansalam.wordpress.com/2013/12/19/mtu-difference-between-cisco-and-juniper/

MTU difference between Cisco and Juniper | Irfan Salam

# re: Configuring the Juniper Media, IP & MPLS MTU @ Wednesday, August 30, 2017 11:56 AM

Thank you for any other fantastic article. The place else

may just anyone get that kind of information in such an ideal

way of writing? I've a presentation subsequent week, and

I'm at the look for such info.

IT

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