Display locally originated BGP routes

Displaying the BGP routes originated in the local AS is simple: you just filter the BGP table with a regular expression matching an empty AS path. Displaying routes originated by the local router is tougher. You could use the fact that the local routes have the weight set to 32768:

PE-A#show ip bgp quote-regexp "^$" | inc Network|32768
Network Next Hop Metric LocPrf Weight Path
*> 10.0.1.1/32 0.0.0.0 0 32768 i

This would work if you don’t play with BGP weights in network statements. If you’ve changed the weights, you should filter the routes based on the BGP next-hop: locally originated routes have the next-hop 0.0.0.0 and all other routes should have a non-zero BGP next-hop. To filter BGP routes based on the next-hop you have to:

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Display BGP routes originated in the local AS

The easiest way to display BGP routes originating in the local autonomous system is to use the regular expression ^$ (empty AS-path) in the show ip bgp regexp command, for example:

PE-A#show ip bgp regexp ^$
BGP table version is 10, local router ID is 10.0.1.1
Status codes: s suppressed, d damped, h history, * valid, > best, i - internal,
r RIB-failure, S Stale
Origin codes: i - IGP, e - EGP, ? - incomplete

Network Next Hop Metric LocPrf Weight Path
*> 10.0.1.1/32 0.0.0.0 0 32768 i
r>i10.0.1.2/32 10.0.1.2 0 100 0 i

If you want to apply a show filter to the printout of this command, you have to use the quote-regexp variant; otherwise the rest of the line is interpreted as regular expression. To skip the header explaining the BGP status code (we know them by heart by now, don’t we?), use …

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Configuring lines and terminals

Numerous comments to the "terminal exec prompt" post told me that it might be good to review the line/terminal configuration rules:

  • If you want to configure a permanent line characteristic (for example, international), you should do so in the VTY configuration (see also how the VTY configurations are merged);
  • If you want a temporary change in the characteristic of your current line (VTY or console), use terminal characteristic to enable it or terminal no characteristic to disable it.
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Use the explicit "address-family ipv4" in BGP configurations

If you use multiprotocol BGP (MP-BGP) in your network to support MPLS VPN, IPv6 or IP Multicast over BGP, it's best if you go all the way and configure an explicit ipv4 address family; the resulting BGP configuration is significantly easier to read and understand as the session-specific parameters are clearly separated from the routing-specific parameters and the IPv4 settings are nicely grouped in an explicit section.

To change the format of the BGP configuration, configure the IPv4 address family with the address-family ipv4 unicast router configuration command (the neighbor statements and other configuration settings pertinent to IPv4 configuration are automatically moved into the new address family) or manually activate a BGP neighbor for IPv4 route exchange with the neighbor activate router configuration command.

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CEF and MLS

Harold Arley Morales has asked an interesting question:

What's the difference between Cisco Express Forwarding and Cisco MLS? Is Cisco's implementation of MLS standardized?

CEF is a routing table lookup mechanism. Instead of doing a lookup in the main IP routing table (displayed with the show ip route), the router does a lookup in a fully computed non-recursive version of the IP routing table (Forwarding Information Base - FIB) with layer-2 next-hop information attached to it (adjacency table).

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Another Way to Generate SNMP Trap on High CPU Load

When testing the ERM functionality that together with an EEM applet generates SNMP traps whenever the CPU load exceeds predefined thresholds, I started to wonder what the snmp-server enable traps cpu threshold command does.

After lenghty conversation with uncle Google and Cisco documentation, I found that there's another way to detect and report high CPU load in Cisco IOS: the CPU threshold notification introduced in IOS release 12.3T.

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Generate SNMP trap on high CPU load

Gernot Nusshall has asked an interesting question:

How could I configure the EEM to send an SNMP trap when the cpu load (interval=30sec) is higher than 30%?

My first solution was to enable resource policy traps with the snmp-server enable traps resource-policy, but this feature was introduced in 12.4(15)T and I am not sure everyone is willing to run the latest-and-greatest IOS code. Furthermore, it looks like the traps are sent only for resource policies defined through the ERM MIB; I was not able to generate a trap from a manually configured resource policy. Obviously it was time for another EEM applet.

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Conditional BGP Route Origination

Sebastian Majewski has found an interesting feature: if you use the network route-map BGP configuration command to originate BGP prefixes and use the match conditions within the route-map, BGP inserts the IP prefix in the BGP table only if the source route in the IP routing table satisfies the route-map conditions.

The following text written by Ivan Pepelnjak in 2008 was originally published on CT3 wiki. That web site became unreachable in early 2019. We retrieved the original text from the Internet Archive, cleaned it up, updated it with recent information if necessary, and republished it on ipSpace.net blog on December 28, 2020
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