URL Load Balancing Using Bridged Mode on the Cisco Application Control Engine Configuration Example
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Revision as of 18:37, 4 December 2008
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Goal
Configure basic load balancing (Layer 3) where client traffic enters on one VLAN and is bridged to servers residing on a second VLAN, while the VIP and server IPs reside in the same network.
Design
Clients will send application requests through the multilayer switch feature card (MSFC), which routes them to a virtual IP address (VIP) within the Cisco® Application Control Engine (ACE). The VIP used in this example resides in an ACE context, which is configured with a client VLAN and a server VLAN (Figure 1), and a Bridge Group Virtual Interface (BVI) to tie the VLANs together in a bridge-group. Client requests will arrive at the VIP, and the ACE will pick the appropriate server and then use the destination Network Address Translation (NAT) to send the client request to the server. The server will respond using the interface VLAN of the MSFC as its default gateway to the client. The ACE will then change the source IP to be the VIP and bridge the traffic to the MSFC. The MSFC will then forward the response to the client.
 | Note: | This document will not cover the design and configuration of the basic load balancing configuration; as this is covered in the Basic Load Balancing Using Bridged Mode on the Cisco Application Control Engine Configuration Example. |
Configuration
The Cisco ACE needs to be configured via access control lists (ACLs) to allow traffic into the ACE data plane. After the ACL checks are made, a service policy, which is applied to the interface, is used to classify traffic destined for the VIP. The VIP is associated with a load-balancing action within the multimatch policy. The load-balancing action tells the ACE how to handle traffic that has been directed to a VIP. In this example, all traffic is sent to a server farm, where it is distributed in round-robin fashion to one of five real servers. The ACE configuration occurs in layers, such that it builds from the real IPs to applying the VIP on an interface. Due to this layered structure, it is optimal to create the configuration by working backward from the way the flow is processed. Thus, to enable server load balancing you need to do the following:
- Enable ACLs to allow data traffic through the ACE device, as it is denied by default.
- Configure the IPs of the servers (define rservers).
- Group the real servers (create a server farm).
- Define the virtual IP address (VIP).
- Define how traffic is to be handled as it is received (create a policy map for load-balancing).
- Associate a VIP to a handling action (create a multimatch policy map [a service policy])
- Create client- and server-facing interfaces and a BVI to join them.
- Apply the VIP and ACL permitting client connections to the interface (apply access group and service policy to interface).
To begin the configuration, create an access list for permitting client connections.
ACE-1/bridged(config)# access-list everyone extended permit ip any any ACE-1/bridged(config)# access-list everyone extended permit icmp any any
| Note: | Although this example shows a “permit any any,” it is recommended that ACLs be used to permit only the traffic you want allow through the Cisco ACE. In the past, server load-balancing (SLB) devices have used the VIP and port alone to protect servers. Within the ACE, ACLs are processed first, and thus dropping traffic using an ACL requires fewer resources than dropping it once it passes the ACLs and reaches the VIP. |
The Cisco ACE needs to know the IP address of the servers available to handle client connections. The rserver command is used to define the IP address of the service. In addition, each rserver must be place in service for it to be used. The benefit of this design is that no matter how many applications or services an rserver hosts, the entire real server can be completely removed from the load-balancing rotation by issuing a single “no inservice” or “no inservice-standby” command at the rserver level. This is very beneficial for users needing to upgrade or patch an rserver, because they no longer have to go to each application and remove each instance of the rserver.
ACE-1/bridged(config)# rserver lnx1 ACE-1/bridged(config-rserver-host)# ip add 172.16.3.11 ACE-1/bridged(config-rserver-host)# inservice ACE-1/bridged(config-rserver-host)# rserver lnx2 ACE-1/bridged(config-rserver-host)# ip add 172.16.3.12 ACE-1/bridged(config-rserver-host)# inservice ACE-1/bridged(config-rserver-host)# rserver lnx3 ACE-1/bridged(config-rserver-host)# ip add 172.16.3.13 ACE-1/bridged(config-rserver-host)# inservice ACE-1/bridged(config-rserver-host)# rserver lnx4 ACE-1/bridged(config-rserver-host)# ip add 172.16.3.14 ACE-1/bridged(config-rserver-host)# inservice ACE-1/bridged(config-rserver-host)# rserver lnx5 ACE-1/bridged(config-rserver-host)# ip add 172.16.3.15 ACE-1/bridged(config-rserver-host)# inservice
Now group the rservers to be used to handle client connections using two serverfarms. Again the rservers must be placed inservice. This allows a single instance of an rserver to be manually removed from rotation.
ACE-1/bridged(config)# serverfarm webfarm ACE-1/bridged(config-sfarm-host)# rserver lnx1 ACE-1/bridged(config-sfarm-host-rs)# inservice ACE-1/bridged(config-sfarm-host-rs)# rserver lnx2 ACE-1/bridged(config-sfarm-host-rs)# inservice ACE-1/bridged(config)# serverfarm imagefarm ACE-1/bridged(config-sfarm-host)# rserver lnx3 ACE-1/bridged(config-sfarm-host-rs)# inservice ACE-1/bridged(config-sfarm-host-rs)# rserver lnx4 ACE-1/bridged(config-sfarm-host-rs)# inservice ACE-1/bridged(config-sfarm-host-rs)# exit
Use a class-map to define the VIP where clients will be sending their requests.
ACE-1/bridged(config)# class-map slb-vip ACE-1/bridged(config-cmap)# match virtual-address 172.16.3.101 tcp eq 80
Next define an http class to match URLs requesting images. This is done using a simple http url match on the /image/ directory name. The wildcard allows for any image filename to be matched.
ACE-1/bridged(config)# class-map type http loadbalance match-all images ACE-1/bridged(config-cmap-http-lb)# match http url /images/.*
Next define the action to take when a new client request arrives. In this case we have two possible actions, based on the http matching class defined above requests for images will be sent to the imagefarm, while all other requests will be sent to the web servers in the webfarm.
ACE-1/bridged(config)# policy-map type loadbalance http first-match slb-logic ACE-1/bridged(config-pmap-lb)# class images ACE-1/bridged(config-pmap-lb-c)# serverfarm imagefarm ACE-1/bridged(config-pmap-lb-c)# class class-default ACE-1/bridged(config-pmap-lb-c)# serverfarm webfarm
Since the VIPs and load-balancing actions are defined independently, they must be associated so that the Cisco ACE knows how to handle traffic destined for a VIP. The association is made using a multimatch policy map. Keep in mind that multimatch policy maps are applied to interfaces as service policies.
ACE-1/bridged(config)# policy-map multi-match client-vips ACE-1/bridged(config-pmap)# class slb-vip ACE-1/bridged(config-pmap-c)# loadbalance policy slb ACE-1/bridged(config-pmap-c)# loadbalance vip inservice
At this point the interface VLANs and BVI can be created to interconnect the Cisco ACE to the client side of the network and to the servers.
ACE-1/bridged(config)# interface vlan 30 ACE-1/bridged(config-if)# description “Client Side” ACE-1/bridged(config-if)# bridge-group 3 ACE-1/bridged(config-if)# no shutdown ACE-1/bridged(config-if)# interface vlan 31 ACE-1/bridged(config-if)# description “Server Side” ACE-1/bridged(config-if)# bridge-group 3 ACE-1/bridged(config-if)# no shutdown ACE-1/bridged(config-if)# interface bvi 3 ACE-1/bridged(config-if)# description “client – server bridge group” ACE-1/bridged(config-if)# ip address 172.16.3.5 255.255.255.0
The last step is to apply the ACL and service policy (“policy-map multi-match”) to the client-side interface. Both the access group and service policy are applied on the input side of the interface.
ACE-1/bridged(config)# interface vlan 30 ACE-1/bridged(config-if)# access-group input everyone ACE-1/bridged(config-if)# service-policy input client-vips
| Note: | There is no need to add an access group to the server side, as the Cisco ACE automatically creates pinholes to allow server response traffic to pass back to the client. |
When a client connects to the VIP they download the index.html page from the webfarm servers and all the embedded images from the imagefarm servers. This can be verified using the detailed output of the show service-policy command:
ACE-1/bridged# show service-policy client-vips detail
Status : ACTIVE
Description: -
-----------------------------------------
Interface: vlan 30
service-policy: client-vips
class: slb-vip
VIP Address: Protocol: Port:
172.16.3.101 tcp eq 80
loadbalance:
L7 loadbalance policy: slb-logic
VIP Route Metric : 77
VIP Route Advertise : DISABLED
VIP ICMP Reply : DISABLED
VIP State: INSERVICE
curr conns : 0 , hit count : 83
dropped conns : 2
client pkt count : 524 , client byte count: 45320
server pkt count : 558 , server byte count: 146197
conn-rate-limit : 0 , drop-count : 0
bandwidth-rate-limit : 0 , drop-count : 0
L7 Loadbalance policy : slb-logic
class/match : images
LB action :
primary serverfarm: imagefarm
state: UP
backup serverfarm : -
hit count : 20
dropped conns : 0
class/match : class-default
LB action :
primary serverfarm: webfarm
state: UP
backup serverfarm : -
hit count : 5
dropped conns : 0
Related show Commands
This section provides information you can use to confirm your configuration is working properly.
Certain show commands are supported by the Output Interpreter Tool (registered customers only), which allows you to view an analysis of show command output.
ACE-1/bridged #show arp ACE-1/bridged #show acl ACE-1/bridged #show service-policy client-vips ACE-1/bridged #show serverfarm ACE-1/bridged #show rserver ACE-1/bridged #show stats
Comments
Once you’ve completed the configuration, verify that the Cisco ACE has an Address Resolution Protocol (ARP) response for each rserver and the default Bridge to the client. Check the ACL hits to ensure that client connections are being accepted. Check the service policy output to see the client connection hits, and verify that the server is responding with response packets. The “show” command for serverfarm and rserver can be used to display the exact rserver handling the connection and the amount of work the entire server farm has handled. The “show stats” command provides a higher level of monitoring of ACE load balancing, inspection, probes, and other important metrics. show running-config
ACE-1/bridged# show run
Generating configuration....
access-list everyone line 8 extended permit ip any any
access-list everyone line 16 extended permit icmp any any
rserver host lnx1
ip address 172.16.3.11
inservice
rserver host lnx2
ip address 172.16.3.12
inservice
rserver host lnx3
ip address 172.16.3.13
inservice
rserver host lnx4
ip address 172.16.3.14
inservice
rserver host lnx5
ip address 172.16.3.15
inservice
serverfarm host web
rserver lnx1
inservice
rserver lnx2
inservice
rserver lnx3
inservice
rserver lnx4
inservice
rserver lnx5
inservice
class-map match-all slb-vip
2 match virtual-address 172.16.3.101 any
policy-map type management first-match remote-access
class class-default
permit
policy-map type loadbalance http first-match slb
class class-default
serverfarm web
policy-map multi-match client-vips
class slb-vip
loadbalance vip inservice
loadbalance policy slb
interface vlan 30
description "Client Side"
bridge-group 3
access-group input everyone
service-policy input client-vips
no shutdown
interface vlan 31
description "Server Side"
bridge-group 3
service-policy input remote-access
no shutdown
interface bvi 3
ip address 172.16.3.5 255.255.255.0
description "client - server bridge group"
no shutdown
ip route 0.0.0.0 0.0.0.0 172.16.3.1
