Alcatel Lucent 7750 SR Router High Availability Deployment and Troubleshooting

Alcatel Lucent 7750 SR series business router high availability architecture deployment and operation manual

At the edge of converged IP networks, the Alcatel Lucent 7750 Service Router (SR) series has become the preferred platform for large enterprises, cloud service providers, and operators to build multi service edge networks due to its high switching capacity of up to 9.6 Tbps, 400 Gbps line speed performance brought by FP3 network processors, and high availability features such as Non Stop Routing/On Stop Services. However, the efficient operation of high-performance platforms relies on scientific chassis selection, redundant configuration, routing strategy optimization, and fast fault location capabilities. This article is based on the technical specifications of the 7750 SR series products, systematically sorting out the troubleshooting process from hardware selection, high availability architecture deployment, L2/L3 VPN business configuration to common alarm and performance degradation scenarios in daily operation and maintenance, providing IP/MPLS network engineers with a practical reference that can be directly implemented.

Product Family Overview and Selection Decision

The 7750 SR series offers three chassis forms, covering different capacity requirements from regional aggregation to the core edge:

7750 SR-7:8U height, 5 I/O module slots, exchange capacity of 2 Tbps, throughput of 2976 Mpps. Supports up to 5 100GbE ports or 15 40GbE ports or 100 10GbE ports. Suitable for medium-sized aggregation nodes or enterprise edges.

7750 SR-12:14U height, 10 I/O module slots, exchange capacity of 4 Tbps, throughput of 5952 Mpps. Supports up to 10 100GbE ports, 30 40GbE ports, or 200 10GbE ports. Suitable for large metropolitan area edges or regional cores.

7750 SR-12e: 22U height, 9 I/O module slots (but supports higher density cards), switching capacity of 9.6 Tbps, throughput of 10713.6 Mpps. Supports up to 9 100GbE ports, 27 40GbE ports, or 180 10GbE ports. Suitable for backbone edge and high-density interconnection scenarios.

Core considerations for selection:

Slot and Scalability: Although SR-12e has fewer I/O slots than SR-12 (9 vs 10), its backplane bandwidth is larger and supports higher density 100G cards. If 100G is the main choice in the future, SR-12e will be given priority.

Main control redundancy: All models support dual SF/CPM (Switching and Control Processor Module) redundancy, equipped with Cavium 10 core 1.5 GHz processor and 16 GB DDR3 memory, with default dual Compact Flash storage.

Power supply and heat dissipation: Supports AC/DC redundant power supply, SR-7 and SR-12 are side to rear air ducts, and SR-12e is front to rear air duct, which needs to be matched with the airflow organization in the computer room. The full weight is 70.5 kg, 155.7 kg, and 249.5 kg respectively, and the rack load capacity needs to be confirmed during installation.

Hardware architecture and board type

The 7750 SR adopts a distributed forwarding architecture, where the data plane and control plane are separated to ensure that a failure in one plane does not affect the operation of another plane.

Key components:

SF/CPM (Switching and Control Processor Module): integrates switching matrix and control processing functions. SR-7/12/12e both support dual SF/CPM redundancy, and Non Stop Routing technology is used to maintain protocol sessions during primary and backup switching.

IMM (Integrated Media Module): an integrated line card that integrates FP3 network processors and physical ports. Common models include:

1×100GbE CFP + 10×10GbE SFP+ IMM

3×40GbE QSFP+ + 20×GbE SFP IMM

20×10GbE SFP+ IMM

48×GbE SFP IMM

IOM (Input/Output Module): Similar to IMM, but with slightly lower processing power, typically used for early deployment. It is recommended to directly use IMM for new facilities to achieve optimal performance.

CFP/QSFP+/SFP+optical module: supports full speed from gigabit to 100G, specific models include JL153A（100GBASE‑LR4）、JL155A（40GBASE‑LR4）、JL156A（10GBASE‑SR） Wait, covering short-range multimode to long-range single-mode.

Port density calculation: For example, when SR-12e is equipped with 9 blocks of 1 × 100G+10 × 10G IMM, it can provide 9 100G ports and 90 10G ports; If equipped with a 48 × GbE IMM, it can provide 432 Gigabit ports.

High availability feature deep configuration

The high availability mechanism of 7750 SR is its core competitive advantage, far surpassing simple hardware redundancy.

3.1 Non‑Stop Routing（NSR）

In the event of a control plane failure (such as a primary SF/CPM crash), the backup SF/CPM seamlessly takes over without relying on adjacent routers to assist in recovery.  

Configuration points:

Ensure that both SF/CPMs are installed and in a "hot standby" state (show redundancy shows HA state: hot standby).

Enable NSR: Add the non stop routing command under routing protocol configuration.

Regularly perform manual switching tests (admin redundancy switchover) to verify the backup master control function.

3.2 Non‑Stop Services（NSS）

On the basis of NSR, NSS ensures that the status of VPLS, VLL, IP VPN and other services is not affected during the switching process. The backup master maintains the business forwarding table and session status, and ensures that the business does not lose packets after switching (or packet loss occurs at the sub second level).

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).

Check the redundancy status (show redundancy), if "out-of-sync" is displayed, perform manual synchronization (admin redundancy synchronization).

Check the system logs to confirm if there are any hardware failures (such as SF/CPM fans, memory errors).

6.5 Performance degradation (packet loss or increased latency)

Troubleshooting:

Check the port error count (show port statistics), high CRC or Alignment errors indicate physical layer issues.

Check the queue dropout count (show QoS queue stats). If there is an increase in WRED dropout, it indicates congestion and requires adjustment of shaping parameters or expansion.

Check the CPU utilization (show system CPU), if it continues to be>60%, investigate whether there is routing oscillation or SNMP polling overload.

Software Upgrade and Configuration Management

The 7750 SR supports ISSU (In Service Software Upgrade) and utilizes NSR/NSS features to achieve seamless control plane upgrades without interrupting the data plane.

Upgrade process:

Upload the new image to the backup SF/CPM.

Start the new version on the backup controller and wait for it to synchronize with the main completion status.

Execute admin upgrade to trigger primary backup switch, and the new version becomes the active controller.

Verify the business and protocol status, and upgrade the old controller after confirming that there are no errors.

Configuration management:

Use Command Authorization to assign different permissions to different administrators and audit logs to record all operations.

Configure automatic backup (copy to FTP/TFTP/SFTP server).

Before modifying the configuration, use admin save to save the checkpoint for quick rollback by admin.

SDN and OpenFlow support

The 7750 SR supports the OpenFlow 1.0 and 1.3 specifications, allowing the forwarding plane to be separated from the control plane and flow tables to be issued by external controllers such as Nuage Networks VSC or OpenDaylight. This provides a foundation for network virtualization and business orchestration, suitable for data center interconnection and multi tenant scenarios.

Key points for activation:

Configure OpenFlow instance (openflow) and bind physical or logical ports.

Set the controller IP and connection parameters (TLS or TCP).

Define flow table matching fields and actions (forwarding, discarding, modifying VLANs, etc.).