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Cisco Bug: CSCvv11079 - ISR 4K - EM7455: LTE module linux default MTU 1500 need to be changed to 2000

Last Modified

Sep 30, 2020

Products (1)

  • Cisco 3G Wireless WAN

Known Affected Releases


Description (partial)

ISR with 4G LTE SIM (cellular modem card) if when the negotiated n/w MTU is not honoured by ISP (for example; modem negotiation is at 1500 bytes, but Carrier allows > 1500 byte packet to reach modem (no fragmentation)) then the modem will lock up and not pass traffic.  To recover from this state; would need to reload the cellular modem card in the ISR.

Seen only in very specific environments where the carrier supports 2K MTU and is not honouring the ISR SIM MTU and also has the backhaul network with MTU >2K to allow packets to return greater than the MTU of the ISR SIM MTU.
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