IPv6 BNG Packet Flow Reference Guide RA (/64) vs DHCPv6 Prefix Delegation (/56)  This document explains the end-to-end IPv6 packet flow in a Broadband Network Gateway (BNG), clearly separating the roles of Router Advertisement (RA) for the access link and DHCPv6 Prefix Delegation (PD) for subscriber network allocation.  The flow is aligned with real-world ISP deployments using IPoE or PPPoE access models.  1. Subscriber Session Creation When a subscriber connects (IPoE or PPPoE), the BNG creates a subscriber session containing IPv4 context, an IPv6 link (/64), and an IPv6 delegated prefix (/56).  2. Router Solicitation (RS) The CPE sends an ICMPv6 Router Solicitation (RS) to ff02::2 (All Routers) asking for IPv6 router presence.  3. Router Advertisement (RA) – /64 Link Prefix The BNG responds with an ICMPv6 Router Advertisement containing a /64 prefix. This prefix is used only for the WAN-side IPv6 address and Neighbor Discovery. It is equivalent to an IPv4 WAN ...

 

 

  Interface Type Used in Datacenter? Scalability Typical Use Case VLAN-Based Less Low/Medium Small DC, MPLS EVPN VLAN Bundle No (Not recommended) High but no separation Metro Ethernet SP VLAN-Aware Bundle YES, MOST WIDELY USED Very High Modern VXLAN/EVPN DC EVPN supports three service models for L2 services. They define how VLANs map to EVPN instances and how NLRI is encoded. A. VLAN-Based Service Interface (VSI-1:1) One VLAN = One EVI (one bridge-domain) Each VLAN/VNI has its own Route-Distinguisher (RD), Route-Target (RT), MAC table, etc. Most granular , simpler to isolate. ✔ Widely used in multi-tenant DC EVPN-VXLAN . B. VLAN-Bundle Service Interface (port-based) Multiple VLANs on a port mapped to one single BD/EVI . The system DOES NOT track which MAC belongs to which VLAN → all treated as a single broadcast domain. Rare in modern DCs. ✔ Used sometimes in L2VPN service provider networks (Port-based E-LAN). C. VLAN-Aware Bun...

SCENARIO — 3 LEAF FABRIC    Spine1 (PIM-SSM)      /      |       \ Leaf1    Leaf2    Leaf3 (VTEP1) (VTEP2)  (VTEP3) Participating VTEPs in VNI 10010 Leaf1 → YES Leaf2 → YES Leaf3 → NO (this leaf does not have VLAN 10/VNI 10010) Assigned multicast group: G = 232.1.1.10 Step 1 — Each VTEP advertises IMET Route-Type 3 Leaf1 advertises: IMET: VNI 10010, mcast 232.1.1.10, VTEP=10.1.1.1 Leaf2 advertises: IMET: VNI 10010, mcast 232.1.1.10, VTEP=10.1.1.2 Leaf3 DOES NOT advertise IMET for VNI 10010 because it has no VLAN/VNI for it. Step 2 — BGP delivers IMET routes to all VTEPs All VTEPs (Leaf1/Leaf2/Leaf3) receive: 2 IMET RT-3 routes(one from Leaf1, one from Leaf2) BUT receiving IMET ≠ joining multicast. Step 3 — How each leaf behaves 1. Leaf1 Has VLAN10 → YES participates Receives IMET from Leaf2 → Joins (S=10.1.1.2, G=232.1.1.10) 2. Leaf2 Has VLAN10 → YES participates Receives IMET from Leaf1 → Joins (S=10...

  Type-2 Route Type-5 Route

In a BGP EVPN VXLAN fabric, route leaking is used to selectively allow communication between otherwise isolated Tenant VRFs. This is typically implemented on a Border Leaf (BL) or a dedicated Service Leaf. Here is an example topology explaining how VRF-Tenant-A communicates with VRF-Shared-Services. Example Topology: Route Leaking We have three main components: 1.Leaf 1 & Leaf 2: Host VTEPs where Tenant A's end devices connect (e.g., 10.1.1.0/24). They have VRF-Tenant-A. 2.Service Leaf (SL): A dedicated VTEP where Shared Services (e.g., a DNS server 10.0.0.10) connect. It has VRF-Shared-Services. 3.Border Leaf (BL): Connects the VXLAN fabric to the external world and usually manages the route leaking process. The Configuration and Process The communication is controlled using Route Targets (RTs) within BGP EVPN extended communities. Each VRF has unique Import RTs and Export RTs. Initial State (Isolation) VRF-Tenant-A: Export RT: 65000:100 Import RT: 65000:100 VRF-Shared-Service...

  r1-r2-r3 running ospf.. when link between r1-r2 brought down.. what are the sequence? how long it take to converge, how/when the routes will be removed from RIB, how LSA invalidate propagated to R3 When the link between R1 and R2 is administratively brought down, a precise sequence of events ensures the network converges to a new, loop-free topology. Assuming standard OSPF default timers (40-second Dead timer) and no advanced features like BFD or FRR: Sequence of Events Step Action Router Affected Timeframe 1 Interface Down Detected R1 & R2 Immediate 2 Hello Timers Expire R1, R2, and all neighbors 40 seconds (Default) 3 LSA Flush Generated R1 & R2 (Originators) Immediate upon detection (Step 1 or 2) 4 LSA Invalidation Flood R1, R2 -> R3 Sub-second propagation 5 SPF Recalculation R3, and all routers Milliseconds after flood 6 RIB Update R3, and all routers Milliseconds after SPF Detailed Breakdown 1. Interface Brought Down & RIB Removal (Immediate) R1  and...