Configuring Localized Data Policy

Configuration Components

An access list consists of a series of numbered (ordered) sequences of match–action pairs that are evaluated in order, from lowest sequence number to highest sequence number. When a packet matches one of the match conditions, the associated action is taken and policy evaluation on that packets stops. Keep this in mind as you design your policies to ensure that the desired actions are taken on the items subject to policy.

If a packet matches no parameters in any of the sequences in the policy configuration, it is, by default, dropped.

To create an access list, you include the following components in the configuration on a vEdge router:

The following figure illustrates the configuration components for access lists.

General Configuration Procedure

Following are the high-level steps for configuring an access list:

1. Create lists of IP prefixes, as needed:
   vEdge(config)# policy
   vEdge(config-policy)# prefix-list list-name
   vEdge(config-prefix-list)# ip-prefix prefix/length
2. For QoS, map each forwarding class to an output queue, configure a QoS scheduler for each forwarding class, and group the QoS schedulers into a QoS map:
   vEdge(config)# policy class-map
   vEdge(config-class-map)# class class-name queue number
   
   vEdge(config)# policy qos-scheduler scheduler-name
   vEdge(config-qos-scheduler)# class class-name
   vEdge(config-qos-scheduler)# bandwidth-percent percentage
   vEdge(config-qos-scheduler)# buffer-percent percentage
   vEdge(config-qos-scheduler)# drops drop-type
   vEdge(config-qos-scheduler)# scheduling type
   
   vEdge(config)# policy qos-map map-name qos-scheduler scheduler-name
3. For QoS, define rewrite rules to overwrite the DSCP field of a packet's outer IP header, if desired:
   vEdge(config)# policy rewrite-rule rule-name
   vEdge(config-rewrite-rule)# class class-name loss-priority dscp dscp-value
   class-name is one of the classes defined under a qos-scheduler command.
4. Define mirroring parameters:​
   vEdge(config)# policy mirror mirror-name
   vEdge(config-mirror)# remote-dest ip-address source ip-address
5. Define policing parameters:​
   vEdge(config)# policy policer policer-name
   vEdgeconfig-policer)# rate bandwidth
   vEdge(config-policer)# burst bytes
   vEdge(config-policer)# exceed action
6. Create an access list instance:​
   vEdge(config)# policy access-list list-name
7. Create a series of match–action pair sequences:
   vEdge(config-access-list-policy-name)# sequence number
   vEdge(config-sequence-number)#
   The match–action pairs are evaluated in order, by sequence number, starting with the lowest numbered pair and ending when the route matches the conditions in one of the pairs. Or if no match occurs, the default action is taken (either rejecting the route or accepting it as is).
8. Define match parameters for packets:
   vEdge(config-sequence-number)# match match-parameter
9. Define actions to take when a match occurs:
   vEdge(config-sequence-number)# action drop
   vEdge(config-sequence-number)# action count counter-name
   vEdge(config-sequence-number)# action log
   vEdge(config-sequence-number)# action accept class class-name
   vEdge(config-sequence-number)# action accept mirror mirror-name
   vEdge(config-sequence-number)# action accept policer policer-name
10. Create additional numbered sequences of match–action pairs within the access list, as needed.
11. If a packet does not match any of the conditions in one of the sequences, it is rejected by default. If you want nonmatching packets to be accepted, configure the default action for the access list:
    vEdge(config-policy-name)# default-action accept
12. Apply the access list to an interface:
    vEdge(config)# vpn vpn-id interface interface-name
    vEdge(config-interface)# access-list list-name (in | out)
    Applying the access list in the inbound direction (in) affects packets being received on the interface. Applying it in the outbound direction (out) affects packets being transmitted on the interface.
    For QoS, apply a DSCP rewrite rule to the same egress interface:
    vEdge(config)# vpn vpn-id interface interface-name rewrite-rule rule-name
    Note that it is also possible to apply a policerdirectly to an interface, which has the effect of policing all packets transiting the interface, rather than policing only the selected packets that match the access list. You can apply the policer to either inbound or outbound packets:​
    vEdge(config)# vpn vpn-id interface interface-name
    vEdge(config-interface)# policer policer-name (in | out

Structural Components of Configuration for Access Lists

Following are the structural components required to configure access lists. Each one is explained in more detail in the sections below.

policy
  lists
    prefix-list list-name
      ip-prefix prefix/length
  class-map
    class class map map
  qos-scheduler scheduler-name
    class class-name
    bandwidth-percent percentage
    buffer-percent percentage
    drops drop-type
  qos-map map-name
    qos-scheduler scheduler-name
  rewrite-rule rule-name
    class class-name priority dscp dscp-value
  mirror mirror-name
    remote-dest ip-address source ip-address
  policer policer-name
    rate bandwidth
    burst bytes
    exceed action
  access-list list-name
    sequence number
      match
        match-parameters
      action
        drop
        count counter-name
        log
        accept
          class class-name
          mirror mirror-name
          policer policer-name
    default-action
      (accept | drop)
vpn vpn-id
  interface interface-name
    access-list list-name (in | out)
    policer policer-name (in | out)
    rewrite-rule rule-name

Lists

Access lists use prefix lists to group related prefixes. You configure lists under the policy lists command hierarchy on vEdge routers.

QoS Parameters

To configure QoS parameters, first define a classification:

vEdge(config)# policy class-map class class-name queue number

Each interface has eight queues, numbered from 0 through 7. The default scheduling method for all queues is weighted round-robin (WRR). However, queue 0 is reserved for low-latency queuing (LLQ), so any class that is mapped to queue 0 must be configured to use LLQ.

Then configure scheduling and assign a scheduler to a QoS map:

vEdge(config)# policy qos-scheduler scheduler-name
vEdge(config-qos-scheduler)# class class-name
vEdge(config-qos-scheduler)# bandwidth-percent percentage
vEdge(config-qos-scheduler)# buffer-percent percentage
vEdge(config-qos-scheduler)# drops (red-drop | tail-drop)
vEdge(config-qos-scheduler)# scheduling (llq | wrr)

vEdge(config-policy)# qos-map map-name qos-scheduler scheduler-name

Finally, configure DSCP rewrite rules:

vEdge(config)# policy rewrite-rule rule-name class class-name loss-priority dscp dscp-value

Mirroring Parameters

To configure mirroring parameters, define the remote destination to which to mirror the packets, and define the source of the packets:

vEdge(config)# policy mirror mirror-name
vEdge(config-mirror)# remote-dest ip-address source ip-address

Policer Parameters

To configure policing parameters, create a policer that specifies the maximum bandwidth and burst rate for traffic on an interface, and how to handle traffic that exceeds these values:

vEdge(config)# policy policer policer-name
vEdge(config-policer)# rate bps
vEdge(config-policer)# burst bytes
vEdge(config-policer)# exceed (drop | remark)

Sequences

An access list contains sequences of match–action pairs. The sequences are numbered to set the order in which a packet is analyzed by the match–action pairs in the access lists. You configure seqences with the policy access-list sequence command.

Each sequence in an access list can contain one match command and one action command.

Match Parameters

Access lists can match IP prefixes and fields in the IP headers. You configure the match parameters under the policy access-list sequence match command.

Each sequence in an access-list must contain one match command.

For access lists, you can match these parameters:

Action Parameters

When a packet matches the conditions in the match portion of an access list, the packet can be accepted or dropped, and it can be counted. Then, you can classify, mirror, or police accepted packets. You configure the actions parameters with the policy access-list sequence action command.

Each sequence in an access list can contain one action command.

In the action, you first specify whether to accept or drop a matching data packet, and whether to count it:

For a packet that is accepted, the following actions can be configured:

Default Action

If a packet being evaluated does not match any of the match conditions in a access list, a default action is applied to this packet. By default, the packet is dropped. To modify this behavior, include the access-list default-action accept command in the access list.

Applying Access Lists

For an access list to take effect, you must apply it to an interface:

vEdge(config)# vpn vpn-id interface interface-name
vEdge(config-interface)# access-list list-name (in | out)

Applying the policy in the inbound direction (in) affects prefixes being received on the interface. Applying it in the outbound direction (out) affects prefixes being transmitted on the interface.

For an access list that applies QoS classification, apply any DSCP rewrite rules to the same interface to which you apply the access list:

vEdge(config)# vpn vpn-id interface interface-name rewrite-rule rule-name

Note that you can also apply a policer directly to an interface, which has the effect of policing all packets transiting the interface, rather than policing only the selected packets that match the access list. You can apply the policer to either inbound or outbound packets:

vEdge(config)# vpn vpn-id interface interface-name
vEdge(config-interface)# policer policer-name (in | out) interface-name

Interaction between Explicit and Implicit Access Lists

Access lists that you configure through localized data policy using the policy access-list command are called explicit ACLs. You can apply explicit ACLs to any interface in any VPN on the router.

The router's tunnel interfaces in VPN 0 also have implicit ACLs, which are also referred to as services. Some services are enabled by default on the tunnel interface, and are in effect unless you disable them. Through configuration, you can also enable other services. You configure and modify implicit ACLs with the allow-service command:

vEdge(config)# vpn 0
vEdge(config-vpn)# interface interface-name
vEdge(config-interface)# tunnel-interface
vEdge(config-tunnel-interface)# allow-service service-name
vEdge(config-tunnel-interface)# no allow-service service-name

On vEdge routers, the following services are enabled by default: DHCP (for DHCPv4 and DHCPv6), DNS, and ICMP. These three services allow the tunnel interface to accept DHCP, DNS, and ICMP packets. You can also enable services for BGP, Netconf, NTP, OSPF, SSHD, and STUN.

When data traffic matches both an explicit ACL and an implicit ACL, how the packets are handled depends on the ACL configuration. Specifically, it depends on:

• Whether the implicit ACL is configured as allow (allow-service allow-service) or deny (no allow-service service-name). Allowing a service in an implicit ACL is the same as specifying the accept action in an explicit ACL, and a service that is not allowed in an implicit ACL is the same as specifying the drop action in an explicit ACL
• Whether, in an explicit ACL, the accept or deny action is configured in a policy sequence or in the default action.

The following table explains how traffic matching both an implicit and an explicit ACL is handled:

Additional Information

Localized Data Policy