How is packet handled when DF bit is set?

Summary

Packet is fragmented even if DF bit is set.

Question

Why is packet fragmented even if DF bit is set after R5.2.2?

Customer Environment

SZ124 R5.2.2

Resolution

Packet handling with DF bit set and over MTU size through Tunnel is configured by the following flags.

------ TUNNELMGR Information ------
tunnelmgr Service: Enabled
Tunnel Establishment: Disabled
Tunnel IPSec: Disabled
Tunnel Authentication: Enabled
Tunnel Cipher: Disabled
Tunnel Cipher Key Len:
Tunnel Forward Bcast: Disabled
PMTU: Auto
PMTU Discovery: Disabled
Node Affinity: Disabled
Force Fragmentation: Disabled
Offload: Disabled
Dual Tunnels: Disabled

Packet handling condition was changed after R5.2.2 as below

DF	FF	PMTU disc	(packet > MTU)
not set	disabled	disabled	fragment
not set	disabled	enabled	fragment
not set	enabled	disabled	fragment
not set	enabled	enabled	fragment
set	disabled	disabled	fragment
set	disabled	enabled	icmp error + packet drop
set	enabled	disabled	fragment
set	enabled	enabled	fragment

However, Ruckus discussed this function again and rolled back to same behavior as R5.2.1 as below.

DF	FF	PMTU disc	(packet > MTU)
not set	disabled	disabled	fragment
not set	disabled	enabled	fragment
not set	enabled	disabled	fragment
not set	enabled	enabled	fragment
set	disabled	disabled	icmp error + packet drop
set	disabled	enabled	icmp error + packet drop
set	enabled	disabled	fragment
set	enabled	enabled	fragment

This change was made in ER-11149 after R5.2.2 and R6.1.

Article Number:
000012253

Updated:
June 05, 2022 06:09 PM (over 2 years ago)

Tags:
Configuration, Troubleshooting, Known Issues and Workarounds, SmartCell Gateway

Votes:
1

This article is:
helpful
not helpful