Configure Link Bundles for Layer 2 VPNs

An ethernet link bundle is a group of one or more ports that are aggregated together and treated as a single link. Each bundle has a single MAC, a single IP address, and a single configuration set (such as ACLs or QoS).

The advantages of link bundling are:

  • Redundancy - Because bundles have multiple links, the failure of a single link does not cause a loss of connectivity.
  • Increased bandwidth - On bundled interfaces traffic is forwarded over all available members of the bundle aggregating individual port capacity.
There are two types of link bundling supported depending on the type of interface forming the bundle:

  • Ethernet interfaces

  • VLAN interfaces (bundle sub-interfaces)

This section describes the configuration of ethernet and VLAN link bundles for use in Layer 2 VPNs.

Configure Gigabit Ethernet Link Bundle

Cisco IOS XR software supports the EtherChannel method of forming bundles of Ethernet interfaces. EtherChannel is a Cisco proprietary technology that allows the user to configure links to join a bundle, but has no mechanisms to check whether the links in a bundle are compatible.

IEEE 802.3ad encapsulation employs a Link Aggregation Control Protocol (LACP) to ensure that all the member links in an ethernet bundle are compatible. Links that are incompatible or have failed are automatically removed from the bundle.

Cisco NCS 5500 Series Router supports 100G link bundles.

Restrictions

  • All links within a single ethernet link bundle must be configured either to run 802.3ad (LACP) or Etherchannel (non-LACP). Mixed links within a single bundle are not supported.

  • MAC accounting is not supported on Ethernet link bundles.

  • The maximum number of supported links in each ethernet link bundle is 64 .

  • The maximum number of supported ethernet link bundles is 128 .

  • You observe a traffic drop for a few seconds for Layer 2, Layer 3, and BUM traffic when you add bundle members to the existing bundles on the NCS57 line card.

  • On an egress (NCS 5500 Series) router’s NC57 line card, when BUM traffic is sent from the core network to the AC network over a bundle interface, the hash function is not performed on active bundle member interfaces. Rather, a specific bundle pin-down member interface is used for sending BUM traffic.

Configuration Example

To create a link bundle between two routers, you must complete the following configurations:

  1. Create a bundle instance

  2. Map physical interface (s) to the bundle.

Sample values are provided in the following figure.

Figure 1. Link Bundle Topology

For an Ethernet bundle to be active, you must perform the same configuration on both connection endpoints of the bundle.

Configuration


/* Enter the global configuration mode and create the ethernet link bundle */
Router# configure
Router(config)# interface Bundle-Ether 3
Router(config-if)# ipv4 address 10.1.2.3 255.0.0.0
Router(config-if)# bundle maximum-active links 32 hot-standby
Router(config-if)# bundle minimum-active links 1
Router(config-if)# bundle minimum-active bandwidth 30000000
Router(config-if)# exit

/* Map physical interfaces to the bundle */
/* Note: Mixed link bundle mode is supported only when active-standby operation is configured */
Router(config)# interface TenGigE 1/0/0/0
Router(config-if)# bundle id 3 mode on
Router(config-if)# no shutdown
Router(config)# exit

Router(config)# interface TenGigE 1/0/0/1
Router(config-if)# bundle id 3 mode on
Router(config-if)# no shutdown
Router(config-if)# exit

Router(config)# interface TenGigE 1/0/0/2
Router(config-if)# bundle id 3 mode on
Router(config-if)# no shutdown
Router(config-if)# exit

Running Configuration 


Router# show running-configuration
configure
interface Bundle-Ether 3
 ipv4 address 10.1.2.3 255.0.0.0
 bundle maximum-active links 32 hot-standby
 bundle minimum-active links 1
 bundle minimum-active bandwidth 30000000
!
interface TenGigE 1/0/0/0
 bundle-id 3 mode on
!

interface TenGigE 1/0/0/1
 bundle-id 3 mode on
!
interface TenGigE 1/0/0/2
 bundle-id 3 mode on
!

Verification

Verify that interfaces forming the bundle are active and the status of the bundle is Up. 
Router# show bundle bundle-ether 3 
Tue Feb  4 18:24:25.313 UTC

Bundle-Ether1
  Status:                                    Up
  Local links <active/standby/configured>:   3 / 0 / 3
  Local bandwidth <effective/available>:     30000000 (30000000) kbps
  MAC address (source):                      1234.1234.1234 (Configured)
  Inter-chassis link:                        No
  Minimum active links / bandwidth:          1 / 1 kbps
  Maximum active links:                      32
  Wait while timer:                          2000 ms
  Load balancing:                            Default
  LACP:                                      Not operational
    Flap suppression timer:                  Off
    Cisco extensions:                        Disabled
    Non-revertive:                           Disabled
  mLACP:                                     Not configured
  IPv4 BFD:                                  Not configured

  Port                  Device           State        Port ID         B/W, kbps
  --------------------  ---------------  -----------  --------------  ----------
  Te1/0/0/0            Local            Active       0x8000, 0x0000    10000000
      Link is Active
  Te1/0/0/1            Local            Active       0x8000, 0x0000    10000000
      Link is Active
  Te1/0/0/2            Local            Active       0x8000, 0x0000    10000000
      Link is Active

------------------------------------------------------------------------

Associated Commands

Configure VLAN Bundle

Configuration Example

The procedure for creating VLAN bundle is the same as the procedure for creating VLAN sub-interfaces on a physical ethernet interface.

To configure VLAN bundles, complete the following configurations:

  • Create a bundle instance.

  • Create a VLAN interface (bundle sub-interface).

  • Map the physical interface(s) to the bundle.

For a VLAN bundle to be active, you must perform the same configuration on both end points of the VLAN bundle.

Configuration


/* Enter global configuration mode and create VLAN bundle */
Router# configure
Router(config)# interface Bundle-Ether 2
Router(config-if)# ipv4 address 50.0.0.1/24
Router(config-if)# bundle maximum-active links 32 hot-standby
Router(config-if)# bundle minimum-active bandwidth 30000000
Router(config-if)# bundle minimum-active links 1
Router(config-if)# commit

/* Create VLAN sub-interface and add to the bundle */
Router(config)# interface Bundle-Ether 2.201
Router(config-subif)# ipv4 address 12.22.1.1 255.255.255.0
Router(config-subif)# encapsulation dot1q 201
Router(config-subif)# commit

/* Map the physical interface to the bundle */
Router(config)# interface TenGigE 0/0/0/14
Router(config-if)# bundle id 2 mode on
Router(config-if)# no shutdown
Router(config-if)# commit

/* Repeat the above steps for all the member interfaces:
   0/0/0/15, 0/0/0/16 and 0/0/0/17 in this example */

Running Configuration 


configure
interface Bundle-Ether2
 ipv4 address 50.0.0.1 255.255.255.0
 mac-address 1212.1212.1212
 bundle maximum-active links 32 hot-standby
 bundle minimum-active links 1
 bundle minimum-active bandwidth 30000000
!
interface Bundle-Ether2.201
 ipv4 address 12.22.1.1 255.255.255.0
 encapsulation dot1q 201
!
interface TenGigE0/0/0/14
 bundle id 2 mode on
!
interface TenGigE0/0/0/15
 bundle id 2 mode on
!
interface TenGigE0/0/0/16
 bundle id 2 mode on
!
interface TenGigE0/0/0/17
 bundle id 2 mode on
!

Verification

Verify that the VLAN status is UP. 

Router# show interfaces bundle-ether 2.201

Wed Feb  5 17:19:53.964 UTC
Bundle-Ether2.201 is up, line protocol is up 
  Interface state transitions: 1
  Hardware is VLAN sub-interface(s), address is 28c7.ce01.dc7b
  Internet address is 12.22.1.1/24
  MTU 1518 bytes, BW 20000000 Kbit (Max: 20000000 Kbit)
     reliability 255/255, txload 0/255, rxload 0/255
  Encapsulation 802.1Q Virtual LAN, VLAN Id 201,  loopback not set,
  Last link flapped 07:45:25
  ARP type ARPA, ARP timeout 04:00:00
  Last input 00:00:00, output never
  Last clearing of "show interface" counters never
  5 minute input rate 0 bits/sec, 0 packets/sec
  5 minute output rate 0 bits/sec, 0 packets/sec
     2938 packets input, 311262 bytes, 0 total input drops
  - - -
  - - -

Associated Commands

References for Configuring Link Bundles

This section provides references to configuring link bundles. For an overview of link bundles and configurations, see Configure Link Bundles for Layer 2 VPNs.

Characteristics of Link Bundles

  • Any type of Ethernet interfaces can be bundled, with or without the use of LACP (Link Aggregation Control Protocol).

  • Physical layer and link layer configuration are performed on individual member links of a bundle.

  • Configuration of network layer protocols and higher layer applications is performed on the bundle itself.

  • A bundle can be administratively enabled or disabled.

  • Each individual link within a bundle can be administratively enabled or disabled.

  • Ethernet link bundles are created in the same way as Etherokinet channels, where the user enters the same configuration on both end systems.

  • The MAC address that is set on the bundle becomes the MAC address of the links within that bundle.

  • When LACP configured, each link within a bundle can be configured to allow different keepalive periods on different members.

  • Load balancing is done by flow instead of by packet. Data is distributed to a link in proportion to the bandwidth of the link in relation to its bundle.

  • QoS is supported and is applied proportionally on each bundle member.

  • Link layer protocols, such as CDP, work independently on each link within a bundle.

  • Upper layer protocols, such as routing updates and hello messages, are sent over any member link of an interface bundle.

  • Bundled interfaces are point to point.

  • A link must be in the UP state before it can be in distributing state in a bundle.

  • Access Control List (ACL) configuration on link bundles is identical to ACL configuration on regular interfaces.

  • Multicast traffic is load balanced over the members of a bundle. For a given flow, internal processes select the member link and all traffic for that flow is sent over that member.

Methods of Forming Bundles of Ethernet Interfaces

Cisco IOS-XR software supports the following methods of forming bundles of Ethernet interfaces:

  • IEEE 802.3ad—Standard technology that employs a Link Aggregation Control Protocol (LACP) to ensure that all the member links in a bundle are compatible. Links that are incompatible or have failed are automatically removed from a bundle.

    For each link configured as bundle member, information is exchanged between the systems that host each end of the link bundle:

    • A globally unique local system identifier

    • An identifier (operational key) for the bundle of which the link is a member

    • An identifier (port ID) for the link

    • The current aggregation status of the link

    This information is used to form the link aggregation group identifier (LAG ID). Links that share a common LAG ID can be aggregated. Individual links have unique LAG IDs.

    The system identifier distinguishes one router from another, and its uniqueness is guaranteed through the use of a MAC address from the system. The bundle and link identifiers have significance only to the router assigning them, which must guarantee that no two links have the same identifier, and that no two bundles have the same identifier.

    The information from the peer system is combined with the information from the local system to determine the compatibility of the links configured to be members of a bundle.

    Bundle MAC addresses in the routers come from a set of reserved MAC addresses in the backplane. This MAC address stays with the bundle as long as the bundle interface exists. The bundle uses this MAC address until the user configures a different MAC address. The bundle MAC address is used by all member links when passing bundle traffic. Any unicast or multicast addresses set on the bundle are also set on all the member links.


    Note
    It is recommended that you avoid modifying the MAC address, because changes in the MAC address can affect packet forwarding.

  • EtherChannel—Cisco proprietary technology that allows the user to configure links to join a bundle, but has no mechanisms to check whether the links in a bundle are compatible.

Link Aggregation Through LACP

The optional Link Aggregation Control Protocol (LACP) is defined in the IEEE 802 standard. LACP communicates between two directly connected systems (or peers) to verify the compatibility of bundle members. For a router, the peer can be either another router or a switch. LACP monitors the operational state of link bundles to ensure these:

  • All links terminate on the same two systems.

  • Both systems consider the links to be part of the same bundle.

  • All links have the appropriate settings on the peer.

LACP transmits frames containing the local port state and the local view of the partner system’s state. These frames are analyzed to ensure both systems are in agreement.