1 © 2003, Cisco Systems, Inc. All rights reserved. Jan 2003 Improving Availability in Multilayer Switched Networks

1© 2003, Cisco Systems, Inc. All rights reserved.Jan 2003

Improving Availability in Multilayer Switched Networks


Multilayer Network Design

DistributionDistribution

AccessAccess

BackboneBackbone

WANWAN InternetInternet PSTNPSTN

Server FarmServer Farm

Building BlockAdditionsBuilding BlockAdditions

Core


Multi-VLAN Load Balancing Methods

VLAN A and B

VLAN Trunk A&B

VLAN Trunk A&B VLAN Tru

nk A&B

Fwd VLAN B

Block

VLAN A

Fwd VLAN A

Block VLAN B

Layer-2 ModeLoad Balancing

VLAN A and B

VLAN Trunk A&B VLAN Tru

nk A&B

Forwar

d VLAN BForward VLAN A

Layer-3 ModeLoad Balancing

HSRP 1A

HSRP 2s

HSRP 1s

HSRP 2A


First Hop Redundancy Schemes

• Hot Standby Router Protocol (HSRP)

Cisco informational RFC 2281 ( March 1998)

• Virtual Router Redundancy Protocol (VRRP)

IETF Standard RFC 2338 (April 1998)

• Gateway Load Balancing Protocol (GLBP)

Cisco designed, load sharing, patent pending


HSRP

• A group of routers function as one virtual router by sharing ONE virtual IP address and ONE virtual MAC address

• One (Active) router performs packet forwarding for local hosts

• The rest of the routers provide “hot standby” in case the active router fails

• Standby routers stay idle as far as packet forwarding from the client side is concerned


First Hop Redundancy with HSRP

Gateway routers

CL1 CL2 CL3

HSRP ACTIVE HSRP STANDBY HSRP LISTEN

Clients

R1 R2 R3

R1- Active, forwarding traffic; R2, R3 - hot standby, idle

IP: 10.0.0.254MAC: 0000.0c12.3456vIP: 10.0.0.10vMAC: 0000.0c07ac00

IP: 10.0.0.253MAC: 0000.0C78.9abcvIP:vMAC:

IP: 10.0.0.252MAC: 0000.0cde.f123vIP:vMAC:

IP: 10.0.0.1MAC: aaaa.aaaa.aa01GW: 10.0.0.10ARP: 0000.0c07.ac00




VRRP

• Very similar to HSRP

• A group of routers function as one virtual router by sharing ONE virtual IP address and ONE virtual MAC address

• One (master) router performs packet forwarding for local hosts

• The rest of the routers act as “back up” in case the master router fails

• Backup routers stay idle as far as packet forwarding from the client side is concerned


First Hop Redundancy with VRRP

Gateway routers

CL1 CL2 CL3

VRRP ACTIVE VRRP BACKUP VRRP BACKUP

Clients

R1 R2 R3

R1- Master, forwarding traffic; R2, R3 - backup

IP: 10.0.0.254MAC: 0000.0c12.3456vIP: 10.0.0.10vMAC: 0000.5e00.0100

IP: 10.0.0.253MAC: 0000.0C78.9abcvIP:vMAC:

IP: 10.0.0.252MAC: 0000.0cde.f123vIP:vMAC:

IP: 10.0.0.1MAC: aaaa.aaaa.aa01GW: 10.0.0.10ARP: 0000.5e00.0100




GLBP Defined

• A group of routers function as one virtual router by sharing ONE virtual IP address but using Multiple virtual MAC addresses for traffic forwarding

• Provides uplink load-balancing as well as first hop fail-over

• IP Leadership feature


GLBP Requirements

• Allow traffic from a single common subnet to go through multiple redundant gateways using a single virtual IP address

• Provide upstream load-balancing by utilizing the redundant up-links simultaneously

• Eliminate the need to create multiple vLANs or manually divide clients for multiple gateway IP address assignment

• Preserve the same level of first-hop failure recovery capability as provided by HSRP


First Hop Redundancy with GLBP

Gateway routers

CL1 CL2 CL3

GLBP AVG/AVF,SVF GLBP AVF,SVF GLBP AVF,SVF

Clients

R1 R2 R3

R1- AVG; R1, R2, R3 all forward traffic

IP: 10.0.0.254MAC: 0000.0c12.3456vIP: 10.0.0.10vMAC: 0007.b400.0101

IP: 10.0.0.253MAC: 0000.0C78.9abcvIP: 10.0.0.10vMAC: 0007.b400.0102

IP: 10.0.0.252MAC: 0000.0cde.f123vIP: 10.0.0.10vMAC: 0007.b400.0103

IP: 10.0.0.1MAC: aaaa.aaaa.aa01GW: 10.0.0.10ARP: 0007.B400.0101




Campus Access Layer Design

Campus Network

GW= 10.88.50.10GW= 10.88.49.10C

CA

A

D

DB

B

Layer-3 switches at distribution layer

Layer-2 switches at access layer

Better utilization of resources and uplinks

GLBP balances traffic across both layer-3 switches

10.88.49.1010.88.50.10vIP address

vMAC AvMAC C

vMAC BvMAC D


Service Provider Edge

10.88.49.1010.88.50.10vIP address

GW= 10.88.49.10C

CA

A

D

DB

B

RedundantCPE routers

Layer-2 switches at access layer


GLBP balances traffic across both routers SP Network

High Availability for Remote Office

GW= 10.88.50.10

vMAC AvMAC C

vMAC BvMAC D


Server Farm Example

Campus Network

L2 Dual-homed servers for port and switch redundancy Layer-2 switches at

access layer

Layer-3 switches at distribution layer GLBP balances

traffic across both layer-3 switches


10.88.49.10vIP addressSome

application but SLB more appropriate


SLB – Server Load Balancing

• SLB Presents a Virtual Address and Load Balances the Traffic Across Multiple Servers

• Virtual Server: Represents an instance of a server farm

• Real Server: An individual server within the farm

Virtual IP192.168.1.200 192.168.1.1 80

192.168.1.2 80


SLB Benefits

• High performance is achieved by distributing client requests across a cluster of servers.

• Administration of server applications is easierClients know only about virtual servers

No administration is required for real server changes

Maintenance with continuous availability is achieved by allowing physical (real) servers to be transparently placed in or out of service

• Security of the real server is provided because its address is never announced to the external network

Users are familiar only with the virtual IP address

Filtering of unwanted traffic can be based on both IP address and IP port numbers


MSFC2 High Availability Features

• Provides multilayer switching and routing services between switched VLANs

• Dependent on Supervisor

Supervisor reset or failure will reset the MSFC2

• Operates in Dual Router Mode (DRM) or Single Router Mode (SRM)


Dual Router Mode (DRM)

• Both MSFCs online

• Each MSFC independently builds an accurate picture of the Layer 3 network

• The failover mechanism between MSFCs in DRM is the HSRP

• MSFCs maintain nearly identical configurations

• First online is ‘designated router’, second is ‘non-designated router’

Designated router programs the Layer 3 entries in the PFC2s Cisco Express Forwarding (CEF) table


MSFC Config Sync

• Startup and running configurations between the designated (primary) and nondesignated (secondary) MSFCs are synchronized

• The following commands enable MSFC config-sync:

• Configuration of the nondesignated MSFC is accomplished through the use of the alt keyword

MSFC-Sup-15 (config)# redundancyMSFC-Sup-15 (config-r)# high-availability MSFC-Sup-15 (config-r-ha)# config-sync

MSFC-Sup-15 (config-if)# ip address a.b.c.1 x.x.x.0 alt ip address a.b.c.2 x.x.x.0MSFC-Sup-15 (config-if)# standby 10 priority 100 alt standby 10 priority 50


Sample DRM Configuration

DRMhostname DRM!redundancy high-availability config-sync !interface Vlan20 ip address 10.20.1.3 255.255.255.0 alt ip address 10.20.1.2 255.255.255.0 standby ip 10.30.1.4 standby priority 100 alt standby priority 50 no ip redirects!interface Vlan30 ip address 10.30.1.3 255.255.255.0 alt ip address 10.30.1.2 255.255.255.0 standby ip 10.30.1.4 standby priority 100 alt standby priority 50 no ip redirects !end


DRM Challenges

• Each MSFC must have a unique IP address for each VLAN interface

• At least one router (the other MSFC) on each VLAN receives non-RPF traffic when multicast is used

• Requirement for exact configuration parameters on both MSFCs complicates matters


SRM – Single Router Mode

• Single Router Mode (SRM) addresses the drawbacks of the previous HSRP based redundancy scheme

• Only the designated router (MSFC) is visible to the network at any given time

• Non-designated router is booted up completely and participates in configuration synchronization, which is automatically enabled when entering SRM

• Non-designated router interfaces are kept in a "line down" state and are not visible to the network


SRM Requirements

• Both MSFCs must run the same IOS image

• High availability needs to be configured on the SUP

• Routing protocol processes are also created on the non-designated router, but dormant

MSFC-Sup-15 (config)# redundancy MSFC-Sup-15 (config-r)# high-availability MSFC-Sup-15 (config-r-ha)# single-router-mode


Sample SRM Configuration

SRMhostname SRM ! redundancy high-availability single-router-mode!interface Vlan20 ip address 10.20.1.3 255.255.255.0 no ip redirects !interface Vlan30 ip address 10.30.1.3 255.255.255.0 no ip redirects!end


Verify SRM Configuration

• sh redundancy command can be used to verify that SRM is enabled:

• Transition timer is used to ensure routing protocol convergence prior to PFC updates

SRM# show redundancyDesignated Router: 1 Non-designated Router: 2 Redundancy Status: designated Config Sync AdminStatus : enabled Config Sync RuntimeStatus: enabled Single Router Mode AdminStatus : enabled Single Router Mode RuntimeStatus: enabled Single Router Mode transition timer : 120 seconds

262626© 2003, Cisco Systems, Inc. All rights reserved.Jan 2003 262626© 2001, Cisco Systems, Inc. All rights reserved.Presentation_ID

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1 © 2003, Cisco Systems, Inc. All rights reserved. Jan 2003 Improving Availability in Multilayer Switched Networks