Configuring A Switch To Allow Routes With Its Own As Number - Dell PowerConnect B-RX Configuration Manual

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Configuring a switch to allow routes with its own AS number

NOTE
If the filter is referred to by a route map's match statement, the filter is applied in the order in which
the filter is listed in the match statement.
The permit | deny parameter indicates the action the router takes if the filter match is true.
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The <num>:<num> parameter indicates a specific community number to filter. Use this parameter
to filter for a private (administrator-defined) community. You can enter up to 20 community
numbers with the same command.
If you want to filter for the well-known communities "LOCAL_AS", "NO_EXPORT" or
"NO_ADVERTISE", use the corresponding keyword (described below).
The internet keyword checks for routes that do not have the community attribute. Routes without a
specific community are considered by default to be members of the largest community, the
Internet.
The local-as keyword checks for routes with the well-known community "LOCAL_AS". This
community applies only to confederations. The device advertises the route only within the sub-AS.
For information about confederations, refer to
The no-advertise keyword filters for routes with the well-known community "NO_ADVERTISE". A
route in this community should not be advertised to any BGP4 neighbors.
The no-export keyword filters for routes with the well-known community "NO_EXPORT". A route in
this community should not be advertised to any BGP4 neighbors outside the local AS. If the router
is a member of a confederation, the device advertises the route only within the confederation. For
information about confederations, refer to
Configuring a switch to allow routes with its own AS number
BGP rejects routes that contain its own AS number within its AS_PATH attribute to prevent routing
loops. In an VPN hub and spoke topology this can stop legitimate routes from being accepted. In
this release, the allowas-in command eliminates this problem by allowing you to set a parameter
that disables the AS_PATH check function for routes learned from a specified location.
To configure a switch to disable the AS_PATH check function for routes sent to it by its BGP
neighbor for a maximum limit of 3 occurrences of the route, enter the following command at the
BGP configuration level.
BigIron RX(config-bgp-ipv4u)# neighbor 33.33.36.2 allowas-in 3
Syntax: neighbor <IPaddress> allowas-in <asn_limit>
The <IPaddress> variable is the IP address of the neighbor.
The asn_limit value prevents loops by limiting the number of occurrences that the AS number will
be accepted in routes that are received from the specified switch. The maximum limit is 10.
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If you specify permit, the router permits the route into the BGP4 table if the filter match is true.
If you specify deny, the router denies the route from entering the BGP4 table if the filter match
is true.
"Configuring confederations"
"Configuring confederations"
BigIron RX Series Configuration Guide
on page 760.
on page 760.
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