Alcatel Lucent 7750 SR Router High Availability Deployment and Troubleshooting

3.3 Graceful Restart（GR）

As a supplement to NSR, GR allows 7750 SR to notify neighbors that it is in a recovery state after restart, requesting neighbors to maintain routing relationships and avoid network oscillations. GR supporting OSPF, IS-IS, BGP, LDP, and RSVP.

3.4 IP Fast Reroute（FRR）

Pre calculate backup paths for each LSP or IP prefix, complete switching within 50 ms in case of link/node failure, without relying on route convergence, which is the key to ensuring SLA in MPLS TE environment.

Operation and maintenance verification:

Regularly check the Show Router OSPF Neighbor to confirm that the neighbor status is stable.

Use test redundancy to simulate various faults (main control power failure, card unplugging) and verify if the recovery time is within the SLA range (recommended<1 second).

Routing and MPLS Business Deployment

7750 SR supports complete IPv4/IPv6 dual stack routing and MPLS functionality, and is the core engine for enterprise L3VPN, L2VPN, and VPLS services.

4.1 L3 VPN（BGP/MPLS IP VPN）

MPLS L3VPN supporting RFC 2547Bis specification, PE devices distribute VPNv4/v6 routing through MP-BGP.

Supports multiple AS VPNs (Option A/B/C), suitable for cross domain interconnection scenarios.

Supports Multicast VPN (MVPN), including PIM-SM and PIM-SSM modes, and can be deployed for multicast services such as IPTV.

4.2 L2 VPN (VLL and VPLS)

VLL (VPWS): Point to point L2VPN, supporting CCC, SVC, Martini, and Kompella signaling methods.

VPLS (Virtual Private LAN Service): Point to multipoint L2VPN, supporting BGP VPLS and LDP VPLS signaling, suitable for data center interconnection or multi-point enterprise interconnection.

H-VPLS (Hierarchical VPLS): By dividing the access layer and core layer, the scalability of VPLS is greatly improved.

4.3 MPLS TE and FRR

Configure MPLS TE tunnel, specify explicit path and bandwidth requirements.

Enable FRR to provide link/node backup for TE tunnel, ensuring recovery within 50 ms.

Supports RSVP-TE and static TE.

Example configuration idea (L3VPN):

Configure global MPLS and LDP/RSVP.

Create VRF instances on PE, bind interfaces and RD/RT.

Configure BGP VPNv4 address family and activate MP-BGP neighbors.

Configure static routing or IGP on the CE side to communicate with PE.

QoS and Traffic Management

The hierarchical QoS (HQQoS) of 7750 SR is the core of providing differentiated services, supporting multi-level scheduling based on ports, user groups, users, and services.

Key functions:

Classification and tagging: Classify traffic based on L2/L3/L4 information (such as VLAN ID, IP priority, DSCP, TCP/UDP ports), support ACL and policy routing.

Congestion avoidance: Supports WRED/RED, sets different dropout curves for different queues, and protects high priority services.

Bandwidth guarantee: Each port can be configured with multiple queues, each queue independently shaped and rate limited. Support commitment rate (CAR) and peak rate (PIR).

MPLS TE Collaboration: TE tunnels are linked with HQQoS to achieve tunnel based bandwidth reservation.

Deployment suggestion: Allocate high priority queues for VoIP services and set minimum bandwidth guarantee; Set up a best effort queue for Internet data services, allowing for bursts but limiting peak hours.

Common fault scenarios and systematic troubleshooting

6.1 BGP Neighbor Interruption

Phenomenon: The neighbor status changes from Established to Idle or Active.

Troubleshooting steps:

Check physical link and IP connectivity (ping neighbor addresses).

Verify whether TCP port 179 is blocked by ACL or firewall.

Check BGP configuration: whether the AS number, update source address, and authentication password (MD5) are consistent.

View BGP status and error logs (show router bgp neighbor<ip>log).

If GR is enabled, confirm that the neighbor also supports GR and the Graceful Restart Timer has not timed out.

6.2 MPLS LSP Unavailable

Phenomenon: Show router MPLS LSP displays Down.

Troubleshooting:

Check LDP/RSVP neighbor status (show router ldp session/show router rsvp neighbor).

Confirm label distribution is normal, show router ldp bindings to view prefix labels.

If TE LSP, check if there are any link interruptions or insufficient bandwidth in the explicit path that prevent it from being established.

Use LSP Ping (oam lsp ping) to test tunnel accessibility.

6.3 VPLS MAC table oscillation or service failure

Phenomenon: MAC addresses frequently migrate under VPLS instances, or CE cannot communicate with each other.

Troubleshooting:

Check the VPLS horizontal segmentation rules and confirm that PW is not used as the broadcast source for loop protection.

Check the MAC table (show service id<id>fdb detail), if there are a large number of unknown unicast, it may be vulnerable to broadcast attacks.

Check the MTU setting of VPLS to ensure consistency at both ends (especially when QinQ is enabled).

Use L2 traceroute (oam l2 traceroute) to locate the PW fault point.

6.4 Failure of main control switching or service interruption

Phenomenon: After manual switching, the business is interrupted for more than a few seconds, or the backup controller cannot take over.

Troubleshooting:

Confirm that the backup main control software version is completely consistent with the main one (show version).