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BGP Troubleshooting
Investigate Cisco BGP session failures, missing prefixes and unexpected path selection using neighbour, policy and forwarding evidence.
Devices supported
across the UK
Client locations
supported
Traffic handled
at peak time
Average
response time
Average response is not a resolution time or a contractual guarantee. Support scope and response commitments are agreed for each engagement.
BGP troubleshooting starts by separating a failed session, a missing route and a forwarding problem. They can produce similar user symptoms, but they require different evidence and different corrective actions. MCI Network Services investigates Cisco BGP incidents for internet edges and private interconnects, working with customer teams and providers to identify the failure without making broad, unreviewed changes to a live routing policy.
Cisco-focused engineering
Design around the platform, traffic and failure behaviour you actually operate.
Change with evidence
Use pre-checks, acceptance criteria and a documented route back.
Operational handover
Keep the configuration, diagrams and responsibilities understandable after delivery.
Define the symptom and its boundaries
We establish what stopped working, when it was first observed and which destinations or applications are affected. A provider alarm, a route withdrawal and an application error may occur at different times. We record those distinctions rather than assuming the first alert identifies the beginning of the fault.
Useful starting information includes a redacted topology, affected prefixes, peer addresses and recent changes. We also ask whether one direction of traffic still works and whether a backup path is carrying service. This helps distinguish a complete connection loss from a policy change affecting selected networks. Sensitive configuration and captures should use an agreed transfer route, not an unrestricted public form.
Standards & partnerships
Confidence in the team behind your network.
Cisco Partner
Cisco Meraki
Cyber Essentials
Cyber Essentials PlusMCI Network Services is operated by Proxar Ltd. Certifications apply to the certified legal entity and the scope of its certificates. View accreditation information
Check the session before changing the routing policy
For a session that is not established, we examine underlying reachability, interface state, addressing, the TCP connection and peer configuration. Autonomous-system mismatches, authentication issues, access controls and multihop prerequisites can all prevent a session from forming. The investigation follows the observed state instead of guessing which command might restore it.
We compare evidence from both ends where possible. A local timeout can have several causes, and the remote team may see a more specific rejection. Provider coordination is therefore part of the service, but it does not transfer the carrier’s repair obligations to MCI. We make the evidence clear enough for the responsible team to act.
A useful starting point
Not sure where to start?
Bring the requirement. We will help you define the engineering work.
Trace a missing prefix through the policy
An established neighbour does not mean that a particular prefix has been accepted. We check whether the route is being originated, advertised by the peer, received locally, permitted by policy and selected for installation. Prefix filters, maximum-prefix events, address-family configuration and validation policy are reviewed at the relevant stage.
We avoid removing all filters to test a theory. A controlled policy examination or narrowly scoped test is safer and produces better evidence. Where a provider rejects a legitimate advertisement, we compare the intended origin and registration information with its requirements. The correction may be administrative rather than a router configuration change.
Different environments. The same care.
Built around the work
your network supports.
Finance, banking and the wider private sector. We start with the systems and people that depend on your connections.
Finance & banking
Market-data paths, routing and provider coordination on clients’ behalf.
Financial-market services ↗Offices & multi-site teams
Reliable access between people, workplaces and business applications.
Office network design ↗Data centres & cloud
Network boundaries, workload connections and operational ownership.
Data centre networks ↗Separate the BGP table from forwarding
A route can exist in BGP without being the active route used for traffic. Another source may win, a next hop may be unreachable or a more-specific prefix may direct traffic elsewhere. We inspect the installed routing and forwarding state, not only the list of received BGP paths.
The return direction matters too. Stateful firewalls, NAT and private partner policies can make an asymmetric route fail even when every router has a destination entry. We trace representative traffic through those boundaries and distinguish network reachability from DNS, entitlement or application problems. In market-data environments, a healthy BGP session does not establish that multicast delivery or feed recovery is healthy.
Investigate intermittent changes
Flapping sessions and unstable paths need a time-based investigation. We correlate routing events with interface errors, circuit alarms, control-plane load and configuration activity. BFD events, where deployed, are examined alongside BGP rather than treated as proof of the underlying cause on their own.
We also consider whether an automatic preference change is behaving as designed but exposing an application dependency. For example, a backup path may use a different translated source address. The resulting failure is not necessarily a BGP defect. The investigation should explain the relationship between the route event and the business symptom.
Restore service without losing the evidence
An urgent incident may require a temporary workaround before the full cause is established. We agree the scope, risk and rollback with the customer, retain the pre-change evidence and record why the action was taken. A workaround that restores connectivity is labelled as such until its long-term suitability is reviewed.
Broad session resets can interrupt unrelated traffic and erase useful state. We use them only when justified by the evidence and change authority. Supported refresh or targeted actions may be less disruptive, but their effect is checked for the actual platform. The aim is to restore useful service while preserving a defensible explanation of what happened.
Finish with findings the business can use
The investigation report separates confirmed facts, plausible contributing factors and unresolved questions. It identifies any provider action, configuration correction or monitoring improvement still required. Where resilience was lost without a total outage, that is recorded as a finding rather than dismissed because users eventually reconnected.
MCI can provide a focused incident engagement or a broader BGP routing review after stabilisation. Service hours, response commitments and access arrangements are agreed for the engagement. The outcome should be a clearer network and a practical prevention plan, not simply a closed ticket saying that the neighbour is up again.
Talk to a specialist
What does your network need next?
Tell us what you are planning, changing or trying to improve. We will help define a practical next step and the engineering scope.
+44 203 196 6566Choose option 1
sales@proxar.co.ukUK-wide service.
Most of our engineers are based in Kent, with a focus on London, Sussex, Essex and Berkshire.
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