Last Modified: Sep 13, 2023
Affected Product(s):
BIG-IP All
Known Affected Versions:
12.1.2, 12.1.3, 12.1.3.1, 12.1.3.2, 12.1.3.3, 12.1.3.4, 12.1.3.5, 12.1.3.6, 12.1.3.7, 12.1.4, 12.1.4.1, 12.1.5, 12.1.5.1, 12.1.5.2, 12.1.5.3, 12.1.6, 13.0.0, 13.0.0 HF1, 13.0.0 HF2, 13.0.0 HF3, 13.0.1, 13.1.0, 13.1.0.1, 13.1.0.2, 13.1.0.3, 13.1.0.4, 13.1.0.5, 13.1.0.6, 13.1.0.7, 13.1.0.8, 13.1.1, 13.1.1.2, 13.1.1.3, 13.1.1.4, 13.1.1.5, 13.1.3, 13.1.3.1, 13.1.3.2, 13.1.3.3, 14.0.0, 14.0.0.1, 14.0.0.2, 14.0.0.3, 14.0.0.4, 14.0.0.5, 14.0.1, 14.0.1.1, 14.1.0, 14.1.0.1
Fixed In:
15.0.0, 14.1.0.2, 13.1.3.4
Opened: Apr 20, 2018 Severity: 3-Major
The MTU of the tmm_bp kernel interface may be out-of-sync with the value of sys db vlan.backplane.mtu as well as out-of-sync with the MTU displayed by the following command: tmsh show /net vlan all-properties -hidden.
From the data plane perspective, this issue can cause excessive IP fragmentation on tmm_bp VLAN and high CPU usage. In some cases it also causes packet loss. From the config perspective, this issue has a few smaller impacts: -- Fragmented packets on the tmm_bp interface for those packets greater in length than the actual MTU of this interface as given by the kernel in response to the command: ip address list dev tmm_bp | egrep -i mtu or $ifconfig tmm_bp. Note: This has no impact to the running system. Fragmented packets are reassembled in order for TCP clients of the tmm_bp interface. -- The sys db variable vlan.backplane.mtu may be out-of-sync with the value of the MTU of the kernel interface tmm_bp as given by either of the following commands: ip address list dev tmm_bp ifconfig tmm_bp -- Similarly, the sys db variable vlan.backplane.mtu may be out-of-sync with the value of the MTU of the Net::Vlan tmm_bp as returned by the command: tmsh show net vlan -hidden tmm_bp Paraphrasing: The value of VLAN tmm_bp MTU (as found in vlan.backplane.MTU) is not applied to the corresponding kernel interface.
This issue occurs on first-boot after upgrading to versions later than v12.1.1 HF1.
A series of subsequent restarts rolls the correct setting by issuing the following commands, in sequence: tmsh stop sys service all tmsh start sys service all To verify the setting is correct, issue the command: ip addr show dev tmm_bp ; tmsh show net vlan -hidden tmm_bp \; list sys db vlan.backplane.mtu
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