eBGP neighbor without a prefix limit
At a glance
Base severity
Area
Platform
Evidence level
Benchmark reference
Reads the export, not the device
ConfigProof reads a configuration export. This control is evaluated against the objects in that file, and it reports what the file says. It does not connect to the device and sees no traffic, so a finding here describes the configuration, not what the firewall is doing right now.
Why it matters
A neighbor that leaks a full table or a misconfiguration can fill the router's table and memory and take its routing down with it.
How to fix it
Web interface
The steps below are written for the web interface. A finding raised on your own export carries the same steps with your object names filled in.
- Configure neighbor <neighbor> maximum-prefix <limit> under router bgp (on NX-OS, maximum-prefix <limit> under the neighbor's address family), with a limit above what the neighbor normally sends.
Command line
Cisco IOS-XE CLI
configure terminalrouter bgp <asn>neighbor <neighbor> maximum-prefix <limit>endwrite memory
An example. Values in angle brackets are yours to supply; a finding on your own export fills in the names it read. Typed in configuration mode; copy running-config startup-config saves it, with no separate commit. Read every line first.
Read it back
show ip bgp neighbors <neighbor> | include prefixValues to fill in3
- <asn>
- This router's BGP AS number
- <neighbor>
- The neighbor's address
- <limit>
- The most prefixes this neighbor may send
Before you type it1
- Written from the Cisco IOS-XE 17 and NX-OS 9 and 10 command references and not run on a device: read each line before you paste it.
How to confirm the fix
- On the router (read only): show ip bgp neighbors <neighbor>, and confirm the maximum prefixes limit beside the prefixes received.
Limits
- An iBGP neighbor is not judged; a neighbor that inherits a peer group or template the configuration does not hold is not judged.
Compliance references
No benchmark recommendation is mapped to this control in this version.
See it on your own firewall
One complete analysis of one firewall costs nothing and needs no card.