Configuring AS-path Lists

You can specify an AS-path list filter on BGP routes. Each filter is an access-list (ACL) based on regular expressions.

Example:

Create a BGP AS-path list using a regular expression.

switch# configure terminal
switch(config)# ip as-path access-list AllowAS permit 64510
switch(config)# ip as-path access-list AllowAll permit .*
switch(config)# ip as-path access-list AllowFrom_AS_100 permit ^100_[0-9]*$

switch(config)# router bgp 65000
switch(config-router)# neighbor 192.0.2.1 remote-as 65535
switch(config-router-neighbor)# address-family ipv4 unicast
switch(config-router-neighbor-af)# filter-list AllowAS in

Diagram

Classes

route_control (vxlan.overlay_extensions)

Name	Type	Constraint	Mandatory	Default Value
ip_as_path_access_lists	List	[ip_as_path_access_lists]	No

ip_as_path_access_lists (vxlan.overlay_extensions.route_control)

Name	Type	Constraint	Mandatory	Default Value
name	String	Regex: ^[A-Za-z0-9-_]{1,63}$	Yes
entries	List	[entries]	Yes

entries (vxlan.overlay_extensions.route_control.ip_as_path_access_lists)

Name	Type	Constraint	Mandatory	Default Value
seq_number	Integer	min: 1, max: 4294967294	Yes
operation	Choice	permit, deny	Yes
bgp_as_paths_regex	String		Yes

Examples

Example-1

This example will create an ip as-path named AllowAS with an entry 10 which permit BGP routes with the AS number 64510.

This ip AS-path list will be used in the group named ipaspath_RCtrlGrp. This group is consumed by one switch named netascode-leaf1.

ip as-path access-list AllowAS seq 10 permit "64510"

---
vxlan:
  overlay_extensions:
    route_control:
      ip_as_path_access_lists:
        - name: AllowAS
          entries:
            - seq_number: 10
              operation: permit
              bgp_as_paths_regex: '64510'
      groups:
        - name: ipaspath_RCtrlGrp
          ip_as_path_access_lists:
            - name: AllowAS
      switches:
        - name: netascode-leaf1
          groups:
            - ipaspath_RCtrlGrp

Example-2

This example will create an ip as-path named AllowAll with an entry 10 which permit all BGP routes.

This ip AS-path list will be used in the group named ipaspath_RCtrlGrp. This group is consumed by one switch named netascode-leaf1

ip as-path access-list AllowAll seq 10 permit ".*"

---
vxlan:
  overlay_extensions:
    route_control:
      ip_as_path_access_lists:
        - name: AllowAll
          entries:
            - seq_number: 10
              operation: permit
              bgp_as_paths_regex: '.*'
      groups:
        - name: ipaspath_RCtrlGrp
          ip_as_path_access_lists:
            - name: AllowAll
      switches:
        - name: netascode-leaf1
          groups:
            - ipaspath_RCtrlGrp

Example-3

This example will create an ip as-path named AllowFrom_AS_100 with an entry 10 which permit all BGP routes.

This ip AS-path list will be used in the group named ipaspath_RCtrlGrp. This group is consumed by one switch named netascode-leaf1

ip as-path access-list AllowFrom_AS_100 seq 10 permit "^100_[0-9]*$"

---
vxlan:
  overlay_extensions:
    route_control:
      ip_as_path_access_lists:
        - name: AllowFrom_AS_100
          entries:
            - seq_number: 10
              operation: permit
              bgp_as_paths_regex: '^100_[0-9]*$'
      groups:
        - name: ipaspath_RCtrlGrp
          ip_as_path_access_lists:
            - name: AllowFrom_AS_100
      switches:
        - name: netascode-leaf1
          groups:
            - ipaspath_RCtrlGrp

Note In the ip as-path access-list command, the carat (^) starts the input string and designates AS" The underscore (_) means there is a a null string in the string that comes after AS 100" The [0-9]* specifies that any connected AS with a valid AS number can pass the filter. The advantage with the [0-9]* syntax is that it gives you the flexibility to add any number of ASs without a modification to this command string. For additional information, see AS-Regular Expression.