Internetwork Expert s CCNP Bootcamp. Gateway Redundancy Protocols & High Availability. What is High Availability?

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1 Internetwork Expert s CCNP Bootcamp Gateway Redundancy Protocols & High Availability What is High Availability? Ability of the network to recover from faults in timely fashion Service availability time (e.g. 5 nines) Requires redundancy (nodes, links, etc.) Layered implementation Physical layer (SONET), L2 (STP), L3 (IGP) Redundancy should be planned based on target recovery time Excessive redundancy slows convergence Copyright 2010 Internetwork Expert

2 What is High Availability? (cont.) Hierarchical design separates network modules Recovery in one module does not affect other modules Different technologies could be used E.g. IGP recovery in core First Hop Redundancy in Access Layer Technologies need to be synchronized E.g. FHRP selected GW should be aligned with STP root What is Gateway Redundancy? End hosts typically do not route into the network, they default to their gateway If the gateway is down, connectivity is lost First Hop/Gateway Redundancy allows another device to take over for a host s default gateway if it goes down Transparent to the end host No need for dual gateways in DHCP Copyright 2010 Internetwork Expert

3 IP over Ethernet Review ARP is the glue When a HostA wants to communicate with HostB via IP If HostB is on my subnet Check the ARP cache for HostB s MAC If no MAC, ARP for HostB If HostB is not on my subnet Check the ARP cache for gateway s MAC If no MAC, ARP for gateway Network Failure and FHRPs Copyright 2010 Internetwork Expert

4 How Gateway Redundancy Works Multiple routers bundled in a group Group represents virtual gateway All routers know virtual gateway IP Active physical router responds to ARP Virtual MAC used in ARP responses Hosts configured with default gateway IP equal to virtual IP Routers exchange keepalive messages Once active router goes down another one takes it place Gateway Redundancy Protocols Three protocols Same major functionality Difference enhancements Different behind the scenes communication Hot Standby Router Protocol (HSRP) Virtual Router Redundancy Protocol (VRRP) Gateway Load Balancing Protocol (GLBP) Copyright 2010 Internetwork Expert

5 HSRP Overview Hot Standby Router Protocol Cisco proprietary Communication via UDP multicast to at port 1985 Uses active/standby routers Active forwards for virtual MAC Standby checks to make sure active is up If down take over the MAC standby interface level command VRRP Overview Virtual Router Redundancy Protocol Open standard per RFC 3768 Communication with own multicast transport via IP protocol 112 to Uses master/backup routers Master forwards for virtual MAC Backup checks to make sure master is up If down take over the MAC vrrp interface level command Copyright 2010 Internetwork Expert

6 GLBP Overview Gateway Load Balancing Protocol Cisco proprietary Communication via UDP multicast at port 3222 Provides load balancing One virtual IP address Multiple virtual MAC addresses Active Virtual Gateway (AVG) Responds with virtual MACs Active Virtual Forwarder (AVF) Handles particular virtual MAC AVFs backup each other AVFs have weights assigned Advanced FHRP Features Multiple groups per interface Authentication Preemption Interface Tracking and Enhanced Object Tracking IP SLA integration Copyright 2010 Internetwork Expert

7 Object Tracking Allows changing gateway priority based on tracked object state Select activate gateway based on network conditions Tracked objects could be Routes in RIP, IP SLA Operations, Boolean combinations GLBP supports weighting decrement based on tracking Object Tracking (cont.) Tracking object syntax track X track x interface track x ip route track x ip sla track x list boolean The command track ip sla links object tracking to IP SLA Operation IP SLA is mainly used for connectivity tracking with FHRP Copyright 2010 Internetwork Expert

8 Object Tracking (cont.) Linking IP SLA operation FHRP Create SLA operation ip sla x Schedule SLA operations ip sla schedule x start-time Create track objects track x ip sla y Configure FHRP to use objects (e.g. HSRP) standby 1 track x FHRP Example SW3 SW /24 VLAN 10 Fa0/13 Fa0/19 Fa0/19 Fa0/13 Fa0/ /24 VLAN 20 Fa0/16 Fa0/16 Fa0/19 Fa0/16 Fa0/19 SW1 Fa0/0 Fa0/1 SW2 Fa0/2 Fa0/0 R /24 R /24 Copyright 2010 Internetwork Expert

9 Non-Stop Forwarding Higher level platforms separate control plane from data plane modules E.g. RSP handles IP Routing exchange Line cards/distributed fabric implement forwarding RSP failure normally paralyzes data-plane forwarding Redundant RSPs reduce the risk of failure Switchover takes time Non-Stop Forwarding (cont) Stateful Switchover with Redundant RSPs When active RSP fails, standby detects it and becomes active Data-plane State is shared between RSPs Control Plane need to be restarted in new RSP Forwarding continues using old data-plane information (CEF table) New RSP initializes and restarts IGP adjacencies After restart, CEF is updated based on new information Copyright 2010 Internetwork Expert

10 Non-Stop Forwarding (cont) Peers should not notice IGP adjacency loss when RSP restarts Otherwise, FIB tables are flushed Requires protocol extension to signal restart Restart bit for EIGRP Local Link Signaling for OSPF BGP Graceful Restart Capability SSO should be enabled per protocol configuration Copyright 2010 Internetwork Expert