04-Layer 3-IP Routing Configuration Guide

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07-Policy-based routing configuration
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Configuring PBR

About PBR

Policy-based routing (PBR) uses user-defined policies to route packets. A policy can specify parameters for packets that match specific criteria such as ACLs. The parameters include the next hop, output interface, default next hop, and default output interface.

Packet forwarding process

The device forwards received packets using the following process:

1.     The device uses PBR to forward matching packets.

2.     If one of the following events occurs, the device searches for a route (except the default route) in the routing table to forward packets:

¡     The packets do not match the PBR policy.

¡     The PBR-based forwarding fails.

3.     If the routing table-based forwarding fails, the device uses the default next hop or default output interface defined in PBR to forward packets.

4.     If the default next hop or default output interface-based forwarding fails, the device uses the default route to forward packets.

PBR types

PBR includes the following types:

·     Local PBR—Guides the forwarding of locally generated packets, such as ICMP packets generated by using the ping command.

·     Interface PBR—Guides the forwarding of packets received on an interface.

Policy

A policy includes match criteria and actions to be taken on the matching packets. A policy can have one or multiple nodes as follows:

·     Each node is identified by a node number. A smaller node number has a higher priority.

·     A node contains if-match and apply clauses. An if-match clause specifies a match criterion, and an apply clause specifies an action.

·     A node has a match mode of permit or deny.

A policy compares packets with nodes in priority order. If a packet matches the criteria on a node, it is processed by the action on the node. If the packet does not match any criteria on the node, it goes to the next node for a match. If the packet does not match the criteria on any node, the device performs a routing table lookup.

Relationship between if-match clauses

On a node, you can specify multiple types of if-match clauses but only one if-match clause for each type.

To match a node, a packet must match all types of the if-match clauses for the node but only one if-match clause for each type.

Relationship between apply clauses

You can specify multiple apply clauses for a node, but some of them might not be executed. For more information about relationship between apply clauses, see "Configuring actions for a node."

Relationship between the match mode and clauses on the node

Does a packet match all the if-match clauses on the node?

Match mode

Permit

Deny

Yes.

·     If the node contains apply clauses, PBR executes the apply clauses on the node.

¡     If PBR-based forwarding succeeds, PBR does not compare the packet with the next node.

¡     If PBR-based forwarding fails, PBR does not compare the packet with the next node.

·     If the node does not contain apply clauses, the device performs a routing table lookup for the packet.

The device performs a routing table lookup for the packet.

No.

PBR compares the packet with the next node.

PBR compares the packet with the next node.

 

 

NOTE:

A node that has no if-match clauses matches any packet.

 

PBR and Track

PBR can work with the Track feature to dynamically adapt the availability status of an apply clause to the link status of a tracked object. The tracked object can be a next hop, output interface, default next hop, or default output interface.

·     When the track entry associated with an object changes to Negative, the apply clause is invalid.

·     When the track entry changes to Positive or NotReady, the apply clause is valid.

For more information about Track-PBR collaboration, see High Availability Configuration Guide.

Restrictions and guidelines: PBR configuration

If a packet destined for the local device matches a PBR policy, PBR will execute the apply clauses in the policy, including the clause for forwarding. When you configure a PBR policy, be careful to avoid this situation.

PBR tasks at a glance

To configure PBR, perform the following tasks:

1.     Enabling VXLAN-mode PBR

Enable VXLAN mode for PBR on VTEPs to direct packets to VXLAN tunnels.

2.     Configuring a policy

a.     Creating a node

b.     Setting match criteria for a node

c.     Configuring actions for a node

3.     Specifying a policy for PBR

Choose the following tasks as needed:

¡     Specifying a policy for local PBR

¡     Specifying a policy for interface PBR

4.     (Optional.) Enabling the PBR logging feature

Enabling VXLAN-mode PBR

About this task

VXLAN-mode PBR enables you to guide packets from a site-facing interface on a VXLAN VTEP to a VXLAN tunnel by using a PBR policy. If VXLAN-mode PBR is not enabled, the PBR policy on a site-facing interface cannot guide packets to a VXLAN tunnel.

Restrictions and guidelines

Enable VXLAN-mode PBR before you apply a PBR policy to a site-facing interface. This task requires PBR to update forwarding entries, which is time-consuming and might cause inadequate table entry resources.

Procedure

1.     Enter system view.

system-view

2.     Enable VXLAN-mode PBR.

ip policy-based-route vxlan-mode enable

By default, VXLAN-mode PBR is disabled.

Configuring a policy

Creating a node

1.     Enter system view.

system-view

2.     Create a node for a policy, and enter its view.

policy-based-route policy-name [ deny | permit ] node node-number

Setting match criteria for a node

Restrictions and guidelines

On a transport network device, you can configure PBR on the Layer 3 interface to guide the forwarding of packets based on VXLAN IDs. On a VXLAN IP gateway, you can configure PBR on the tunnel interface to guide the forwarding of packets based on VXLAN IDs.

Procedure

1.     Enter system view.

system-view

2.     Enter policy node view.

policy-based-route policy-name [ deny | permit ] node node-number

3.     Set match criteria.

¡     Set an ACL match criterion.

if-match acl { acl-number | name acl-name }

By default, no ACL match criterion is set.

The ACL match criterion cannot match Layer 2 information.

When using the ACL to match packets, PBR ignores the action (permit or deny) and time range settings in the ACL.

¡     Set a local QoS ID match criterion.

if-match qos-local-id local-id-value qppb-manipulation

By default, no local QoS ID match criterion is set.

This command takes effect only on HFR cards and only when the TCAM operating mode of the device is routing or mix. For more information about TCAM operating modes, see device management in Fundamentals Configuration Guide.

If you specify the qppb-manipulation keyword, the command applies only to QPPB in which the device acts as a BGP receiver. The device determines that a received packet matches the policy node if the local QoS ID obtained from its matching route entry is identical to the specified local QoS ID criterion. For more information about QPPB, see ACL and QoS Configuration Guide.

¡     Set a VXLAN match criterion.

if-match vxlan-id vxlan-id

By default, no VXLAN match criterion is set.

Configuring actions for a node

About apply clauses

The apply clauses allow you to specify the actions to be taken on matching packets on a node.

The following apply clauses determine the packet forwarding paths in a descending order:

·     apply access-vpn vpn-instance

·     apply next-hop

·     apply output-interface

·     apply default-next-hop

·     apply default-output-interface

PBR supports the types of apply clauses shown in Table 1.

Table 1 Priorities and meanings of apply clauses

Clause

Meaning

Priority

apply precedence

Sets an IP precedence.

This clause is always executed.

apply access-vpn vpn-instance

Sets VPN instances.

If a packet matches a forwarding entry of a specified VPN instance, it is forwarded in the VPN instance.

apply next-hop and apply output-interface

Sets next hops and output interfaces.

Only the apply next-hop clause is executed when both are configured.

apply default-next-hop and apply default-output-interface

Sets default next hops and default output interfaces.

Only the apply default-next-hop clause is executed when both are configured.

The clauses take effect only in the following cases:

·     No next hops or output interfaces are set or the next hops and output interfaces are invalid.

·     The packet does not match any route in the routing table.

apply statistics

Counts successful matches and matching bytes on the policy node.

To include the number of successful matches and matching bytes on a policy node in the statistics displayed by a display command, execute this command.

This clause is always executed for matching packets.

Restrictions and guidelines

For outbound PBR, you can specify only one next hop and the next hop must be directly connected.

If you specify a next hop or default next hop, PBR periodically performs a lookup in the FIB table to determine its availability. Temporary service interruption might occur if PBR does not update the route immediately after its availability status changes.

Configuring actions to modify packet fields

1.     Enter system view.

system-view

2.     Enter policy node view.

policy-based-route policy-name [ deny | permit ] node node-number

3.     Configure actions.

¡     Set an IP precedence.

apply precedence { type | value }

By default, no IP precedence is specified.

Configuring actions to direct packet forwarding

1.     Enter system view.

system-view

2.     Enter policy node view.

policy-based-route policy-name [ deny | permit ] node node-number

3.     Configure actions.

¡     Set VPN instances.

apply access-vpn vpn-instance vpn-instance-name

By default, no VPN instance is specified.

¡     Set next hops.

apply next-hop [ vpn-instance vpn-instance-name ] { ip-address [ direct ] [ track track-entry-number ] }&<1-2>

By default, no next hops are specified.

You can specify a maximum of two next hops for backup in one command line or by executing this command multiple times.

If multiple next hops on the same subnet are specified for backup, the device first uses the subnet route for the next hops to forward packets when the primary next hop fails. If the subnet route is not available, the device selects a backup next hop.

¡     Set output interfaces.

apply output-interface interface-type interface-number [ track track-entry-number ]

By default, no output interfaces are specified.

¡     Set default next hops.

apply default-next-hop [ vpn-instance vpn-instance-name ] { ip-address [ direct ] [ track track-entry-number ] }&<1-2>

By default, no default next hops are specified.

You can specify a maximum of two default next hops for backup in one command line or by executing this command multiple times.

¡     Set default output interfaces.

apply default-output-interface interface-type interface-number [ track track-entry-number ]

By default, no default output interfaces are specified.

Collecting policy node statistics

1.     Enter system view.

system-view

2.     Enter policy node view.

policy-based-route policy-name [ deny | permit ] node node-number

3.     Count successful matches and matching bytes on the policy node.

apply statistics

By default, match counting is disabled on a policy node.

Specifying a policy for PBR

Specifying a policy for local PBR

About this task

Perform this task to specify a policy for local PBR to guide the forwarding of locally generated packets.

Restrictions and guidelines

You can specify only one policy for local PBR and must make sure the specified policy already exists. Before you apply a new policy, you must first remove the current policy.

Local PBR might affect local services such as ping and Telnet. When you use local PBR, make sure you fully understand its impact on local services of the device.

Procedure

1.     Enter system view.

system-view

2.     Specify a policy for local PBR.

ip local policy-based-route policy-name

By default, local PBR is not enabled.

Specifying a policy for interface PBR

About this task

Perform this task to apply a policy to an interface to guide the forwarding of packets received on the interface.

Restrictions and guidelines

You can apply only one policy to an interface and must make sure the specified policy already exists. Before you can apply a new interface PBR policy to an interface, you must first remove the current policy from the interface.

You can apply a policy to multiple interfaces.

When you use interface PBR in conjunction with VXLAN-mode PBR to guide packets on a site-facing interface to a VXLAN tunnel, enable VXLAN-mode PBR before you apply the PBR policy. For more information about VXLAN-mode PBR, see "Enabling VXLAN-mode PBR."

Procedure

1.     Enter system view.

system-view

2.     Enter interface view.

interface interface-type interface-number

3.     Specify a policy for interface PBR.

ip policy-based-route policy-name

By default, no interface policy is applied to an interface.

Enabling the PBR logging feature

About this task

The PBR logging feature helps the administrator locate and fix faults. The feature logs PBR events and sends the logs to the information center. The information center processes the logs according to output rules. For more information about the information center, see Network Management and Monitoring Configuration Guide.

Procedure

1.     Enter system view.

system-view

2.     Enable the PBR logging feature.

ip policy-based-route-log enable

By default, the PBR logging feature is disabled.

Display and maintenance commands for PBR

Execute display commands in any view and reset commands in user view.

 

Task

Command

Display PBR policy information.

display ip policy-based-route [ policy policy-name ]

Display PBR configuration.

display ip policy-based-route setup

Display local PBR configuration and statistics.

display ip policy-based-route local [ slot slot-number ]

Display interface PBR configuration and statistics.

display ip policy-based-route interface interface-type interface-number [ slot slot-number ]

Clear PBR statistics.

reset ip policy-based-route statistics [ policy policy-name ]

 

PBR configuration examples

Example: Configuring packet type-based local PBR

Network configuration

As shown in Figure 1, Router B and Router C do not have a route to reach each other.

Configure PBR on Router A to forward all TCP packets to the next hop 1.1.2.2 (Router B).

Figure 1 Network diagram

Procedure

IMPORTANT

IMPORTANT:

By default, interfaces on the device are disabled (in ADM or Administratively Down state). To have an interface operate, you must use the undo shutdown command to enable that interface.

1.     Configure Router A:

# Configure the IP addresses of HundredGigE 1/0/1 and HundredGigE 1/0/2.

<RouterA> system-view

[RouterA] interface hundredgige 1/0/1

[RouterA-HundredGigE1/0/1] ip address 1.1.2.1 24

[RouterA-HundredGigE1/0/1] quit

[RouterA] interface hundredgige 1/0/2

[RouterA-HundredGigE1/0/2] ip address 1.1.3.1 24

[RouterA-HundredGigE1/0/2] quit

# Configure ACL 3101 to match TCP packets.

[RouterA] acl advanced 3101

[RouterA-acl-ipv4-adv-3101] rule permit tcp

[RouterA-acl-ipv4-adv-3101] quit

# Configure Node 5 for the policy aaa to forward TCP packets to next hop 1.1.2.2.

[RouterA] policy-based-route aaa permit node 5

[RouterA-pbr-aaa-5] if-match acl 3101

[RouterA-pbr-aaa-5] apply next-hop 1.1.2.2

[RouterA-pbr-aaa-5] quit

# Configure local PBR by applying the policy aaa to Router A.

[RouterA] ip local policy-based-route aaa

2.     On Router B, configure the IP address of HundredGigE 1/0/1.

<RouterB> system-view

[RouterB] interface hundredgige 1/0/1

[RouterB-HundredGigE1/0/1] ip address 1.1.2.2 24

3.     On Router C, configure the IP address of HundredGigE 1/0/2.

<RouterC> system-view

[RouterC] interface hundredgige 1/0/2

[RouterC-HundredGigE1/0/2] ip address 1.1.3.2 24

Verifying the configuration

1.     Perform telnet operations to verify that local PBR on Router A operates as configured to forward the matching TCP packets to the next hop 1.1.2.2 (Router B), as follows:

# Verify that you can telnet to Router B from Router A successfully. (Details not shown.)

# Verify that you cannot telnet to Router C from Router A. (Details not shown.)

2.     Verify that Router A forwards packets other than TCP packets through HundredGigE 1/0/2. For example, verify that you can ping Router C from Router A. (Details not shown.)

Example: Configuring packet type-based interface PBR

Network configuration

As shown in Figure 2, Router B and Router C do not have a route to reach each other.

Configure PBR on Router A to forward all TCP packets received on HundredGigE 1/0/1 to the next hop 1.1.2.2 (Router B).

Figure 2 Network diagram

Procedure

IMPORTANT

IMPORTANT:

By default, interfaces on the device are disabled (in ADM or Administratively Down state). To have an interface operate, you must use the undo shutdown command to enable that interface.

1.     Make sure Router B and Router C can reach Host A. (Details not shown.)

2.     Configure Router A:

# Configure the IP addresses of HundredGigE 1/0/2 and HundredGigE 1/0/3.

<RouterA> system-view

[RouterA] interface hundredgige 1/0/2

[RouterA-HundredGigE1/0/2] ip address 1.1.2.1 24

[RouterA-HundredGigE1/0/2] quit

[RouterA] interface hundredgige 1/0/3

[RouterA-HundredGigE1/0/3] ip address 1.1.3.1 24

[RouterA-HundredGigE1/0/3] quit

# Configure ACL 3101 to match TCP packets.

[RouterA] acl advanced 3101

[RouterA-acl-ipv4-adv-3101] rule permit tcp

[RouterA-acl-ipv4-adv-3101] quit

# Configure Node 5 for the policy aaa to forward TCP packets to next hop 1.1.2.2.

[RouterA] policy-based-route aaa permit node 5

[RouterA-pbr-aaa-5] if-match acl 3101

[RouterA-pbr-aaa-5] apply next-hop 1.1.2.2

[RouterA-pbr-aaa-5] quit

# Configure interface PBR by applying the policy aaa to HundredGigE 1/0/1.

[RouterA] interface hundredgige 1/0/1

[RouterA-HundredGigE1/0/1] ip address 10.110.0.10 24

[RouterA-HundredGigE1/0/1] ip policy-based-route aaa

[RouterA-HundredGigE1/0/1] quit

Verifying the configuration

1.     Perform telnet operations to verify that interface PBR on Router A operates as configured to forward the matching TCP packets to the next hop 1.1.2.2 (Router B), as follows:

# Verify that you can telnet to Router B from Host A successfully. (Details not shown.)

# Verify that you cannot telnet to Router C from Host A. (Details not shown.)

2.     Verify that Router A forwards packets other than TCP packets through HundredGigE 1/0/3. For example, verify that you can ping Router C from Host A. (Details not shown.)

 

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