The Art of ISP Convergence: Lessons from Vodafone–Idea Merger

By Admin | 28-10-2025

Preface:

When two large ISPs such as Vodafone and Idea merge in India, global Internet reachability is a technical requirement. Both such operators have dedicated ASNs, address space ranges, backbone networks, and peering or transit arrangements. Pre-Merger Planning - Pre-merge, engineers must plan the consolidation of ASNs, reconcile BGP routing policies and integrate IP address resources without creating route leaks and blackholes. Customers from both legacy networks are reached on a global scale, so all of our upstream and peering need to be checked to make sure they are up to date. In the case of Vodafone Idea merger that would be to merge their routing domains, advertise prefixes uniformly across international exchanges and validate end to end connectivity so that in effect, millions of customers can continue to carry on with internet services during and post the merge.

Scenario

The Vodafone and Idea merger presents significant technical challenges, particularly in maintaining seamless connectivity for millions of customers while integrating two large-scale networks. Ensuring end-to-end reachability under a unified Vodafone–Idea infrastructure requires a phased and carefully controlled approach.

 

For sake as an example please find key points here with: 

 

•  Vodafone AS: 65001, key prefixes: 203.0.113.0/24, 198.51.100.0/24

•  Idea AS: 65002, key prefixes: 203.0.114.0/24, 203.0.115.0/24

•  EBGP link between edge routers: 192.0.2.1 ↔ 192.0.2.2

•  Upstream remain unchanged during transition.

 

Prerequisite taken before ISP merger:

Please try the following steps as preparatory work for ISP Consolidation--

AS strategy

  • Keep both ASNs as of the moment and interconnect them through EBGP (transition period).

  • Switch to One ASN (last phase).

  • Prepare for renumbering with AS change (WHOIS and upstream providers).

IP address space consolidation

  • Unify public IP prefixes, avoid any clashes.

  • Combine or recombine IP pools (e.g., broadband, enterprise, LTE/5G).

  • Update IRR objects. 

BGP policies & route control

  • Consolidate route maps, prefix lists, community tagging guidelines.

  • Change inbound and outbound TE policies (e.g., pre-pending, MEDs, local pref).

  • Check for route leaks.

Peering and upstream agreements

  • Consolidate or renegotiate peering arrangements with IXPs.

  • Consolidate upstream transit providers.

  • Ensure prefixes are understood by all peers and transits.

IBGP & route reflector design

  • Include internal BGP topology (such as route reflectors, confederations if applicable).

  • Scalability: one may be forced to enhance the number of route reflectors.

Network topology and backbone integration

  • Integrate networks at backbone/core level.

  • Match transport/MPLS backbone —Diff the tech (SR-MPLS vs LDP, old gear vs new gear)?

  • Replan core and distribution layers to eliminate loops or asymmetric traffic.

IGP integration (OSPF/IS-IS)

  • Merge IGP domains carefully.

  • Recalculate areas/levels to prevent flooding and bad routeing.

  • Modify redistribution policies IGP-BGP in order to update route.

MPLS VPN services

  • Consolidate VRFs and VPN RTs, no duplicates.

  • Unify policy of allocating labels (label blocks, global/per-target).

  • Update PE-CE configurations without downtime. DNS & service addressing

  • Update authoritative zones for new prefixes.

  • Update reverse DNS (PTR) record.

Security & filtering / Review of your ingress and egress ACLs or filters

  • Ensure you have good anti-spoofing filters (uRPF) deployed.

  • Verify firewall policies and border security

Customer edge (CE) connectivity

  • Ensure that all the customer prefixes are reachable from the new combined backbone.

  • Re-advertise customer BGP sessions (if the customer is multihomed).

  • Be unyielding about no downtime (temporary tunnels are fine).   

    Monitoring & NMS integration

  • Combine NMS, telemetry, SNMP and flow collectors.

  • Harmonize alerting thresholds and policies.

  • Update inventory and config management databases.

    Service-level agreements (SLA) compliance

  • Expect to meet latency, jitter and availability after the merge.

  • Update SLA tracking and reporting systems.

    IPv6 strategy

  • Consolidate IPv6 subnets and routing policies.

  • Verify that ad and neighbor discovery is Ok.

    Testing and validation

  • Run complete route converge and fail over tests.

  • Verify prefix advertisement (show bgp, route servers, RIPE RIS, etc.).

  • Confirm reachability from external monitoring sites (e.g., Looking Glass, RIPE Atlas).

    Let's check configuration part at both ISP end.

     

===================================================================

At Vodafone ISP end ---

Vodafone ISP #
router bgp 65001
 bgp log-neighbor-changes

EBGP with Idea

 neighbor 192.0.2.2 remote-as 65002 
 neighbor 192.0.2.2 description "EBGP peering with Idea"
IBGP with internal RR

 neighbor 10.0.0.2 remote-as 65001
 neighbor 10.0.0.2 update-source Loopback0
  
Networks advertised 

 network 203.0.113.0 mask 255.255.255.0
 network 198.51.100.0 mask 255.255.255.0

Prefix list to control advertisement

 ip prefix-list VODA-OUT seq 5 permit 203.0.113.0/24
 ip prefix-list VODA-OUT seq 10 permit 198.51.100.0/24
 route-map VODA-EXPORT permit 10
  match ip address prefix-list VODA-OUT
 neighbor 192.0.2.2 route-map VODA-EXPORT out

At IDEA ISP end ---

IDEA#
router bgp 65002
 bgp log-neighbor-changes

EBGP with Vodafone

 neighbor 192.0.2.1 remote-as 65001 
neighbor 192.0.2.1 description "EBGP peering with Vodafone"

IBGP within Idea
 neighbor 10.1.1.2 remote-as 65002
 neighbor 10.1.1.2 update-source Loopback0

Networks advertised

 network 203.0.114.0 mask 255.255.255.0
 network 203.0.115.0 mask 255.255.255.0

 Prefix list to control advertisement

 ip prefix-list IDEA-OUT seq 5 permit 203.0.114.0/24
 ip prefix-list IDEA-OUT seq 10 permit 203.0.115.0/24
 route-map IDEA-EXPORT permit 10
  match ip address prefix-list IDEA-OUT
 neighbor 192.0.2.1 route-map IDEA-EXPORT out

During integrated AS --

Merger_ISP#
router bgp 65001
 bgp log-neighbor-changes

IBGP within unified AS

 bgp router-id 10.255.255.1
 bgp cluster-id 65001
neighbor 10.0.0.2 remote-as 65001
 neighbor 10.0.0.2 update-source Loopback0
 neighbor 10.1.1.2 remote-as 65001
 neighbor 10.1.1.2 update-source Loopback0

Upstream providers

 neighbor 198.51.100.2 remote-as 65400
 neighbor 203.0.113.2 remote-as 65500

 Networks advertised

 network 203.0.113.0 mask 255.255.255.0
 network 198.51.100.0 mask 255.255.255.0
 network 203.0.114.0 mask 255.255.255.0
 network 203.0.115.0 mask 255.255.255.0

Unified export policy

 ip prefix-list MERGED-OUT seq 5 permit 203.0.113.0/24
 ip prefix-list MERGED-OUT seq 10 permit 198.51.100.0/24
 ip prefix-list MERGED-OUT seq 15 permit 203.0.114.0/24
 ip prefix-list MERGED-OUT seq 20 permit 203.0.115.0/24
 route-map MERGED-EXPORT permit 10
match ip address prefix-list MERGED-OUT
neighbor 198.51.100.2 route-map MERGED-EXPORT out
 neighbor 203.0.113.2 route-map MERGED-EXPORT out

Ingress filter for validation

ip prefix-list CUSTOMER-IN seq 5 permit 203.0.113.0/24
ip prefix-list CUSTOMER-IN seq 10 permit 198.51.100.0/24
!
route-map CUSTOMER-VALIDATION permit 10
 match ip address prefix-list CUSTOMER-IN
!
neighbor 203.0.113.2 route-map CUSTOMER-VALIDATION in
neighbor 198.51.100.2 route-map CUSTOMER-VALIDATION in
 
Soft reset and route refresh support

neighbor 203.0.113.2 soft-reconfiguration inbound
neighbor 198.51.100.2 soft-reconfiguration inbound

Verification commands

show ip bgp summary
show ip bgp neighbors 203.0.113.2 advertised-routes
show ip bgp neighbors 203.0.113.2 received-routes
show ip bgp neighbors 198.51.100.2 advertised-routes
show ip bgp neighbors 198.51.100.2 received-routes
show ip bgp
show ip route

Conclusion:

Combining two ISPs such as Vodafone and Idea isn’t just a rebranding, or even business exercise – it’s a complex network engineering transformation that requires meticulous planning, validation and execution. If you want to assure global Internet reachability after merger, harmonized Autonomous System (AS) strategy, merged IP prefix advertisements and uniform routing policy are necessary for traffic flow across both legacy and unified networks. The migration from EBGP interconnects between the two ASNs to a common IBGP core would logically also require tight coupling of MPLS backbones, IGP/unite domains, VRF(s), and firewall/security configurations. Route redistribution, prefix filtering, peer relationship agreements and upstream transit changes must be controlled to maintain path consistency and prevent blackholing or looping. Throughout all lifecycle stages, real-time monitoring and prefix validation (such as an elegant way to benchmark the performance) is crucial to enforce SLA and maintain operational stability. The merger of Vodafone-Idea is an indicator that engineering par excellence in routing architecture, policy control and backbone integration form the underpinning to enable scalable, dependable and secure internet delivery to millions of its consumers both domestic as well as global. With network convergence set to be the new normal in telecom, this approach serves as a roadmap for engineering teams working together on how complex, dated infrastructures can be combined into one simplifies sustainable digital platform.