Cisco 2500 Series Routers

Field Notice: Cisco 2500 in Boot Mode with Cisco IOS 11.0(10c) ROM Slow to Transmit IP Packets

August 24, 1999

Products Affected



Cisco 2500

This affects only those routers with Boot ROM Cisco IOS 11.0(10c).

Problem Description

If the following conditions are met, IP traffic will experience significant delays:

  1. The router must be in Boot mode.

  2. The router has Boot ROM Cisco IOS version 11.0(10c). Earlier ROMs are not affected.

  3. The router is communicating via the WAN link using the ip default-gateway command to direct packets.

  4. The addresses on the local and remote side of the WAN link are in different subnets.

Problem Symptoms

When a Cisco 2500 is running in Boot mode, and is communicating with nodes further away than the next hop over the WAN link (that is, a TFTP server or to a host via Telnet), IP traffic will encounter significant delays which seem as though connectivity is lost.

This occurs only in Boot mode with ROM versions Cisco IOS 11.0(10c), not during normal router operation. Other ROM versions do not exhibit this problem.


When a router is operating in Boot mode, it acts solely as an end-station on a network. It does not forward packets from one interface to another. IP traffic which must travel over a WAN link is delayed when the remote and local sides are in different IP subnets. ARP throttling was introduced with CSCdi43596 to correct problems during normal operation, but the side effect is this behavior during Boot mode.

To follow the bug ID link below and see detailed bug information, you must be a registered user and you must be logged in.

View bug details for CSCdm09766 (registered customers only)


There are two workarounds for this problem.

Workaround One

Use a contiguous address range for each side of the WAN link while running the router in Boot mode.

Workaround Two

Configure a dummy ARP entry for the remote router.

For example, you have a local router with IP address and a remote router with IP address Router is to be run in Boot mode for a software upgrade. Configure the following:

local(boot)(confg)# arp 0000.0c12.3456 arpa

The command above will remove the delays introduced by ARP throttling.

For More Information

If you require further assistance, or if you have any further questions regarding this field notice, please contact the Cisco Systems Technical Assistance Center (TAC) by one of the following methods: