Summary
In this post I'll discuss how to set up dual ISP links in a sample scenario using a single Cisco router with
Performance Routing (PfR). Traditionally, dual links could be set up with
Policy-Based Routing (PBR) and
IP-SLA. An example of that
here. The combination of those two would yield fail-over functionality upon loss of one of the two links. It would not provide load-balancing of those links though. PfR provides both.
Scenario
Below is a diagram of the example dual ISP scenario. One connection is to a DSL provider; the other to a wireless ISP (WISP). Available bandwidth on the links is grossly imbalanced, by a factor of 8. A dialer interface (PPOE) to an ATM interface connects the DSL ISP. There is a Gig Ethernet connection to the WISP. Behind the router/firewall are clients on private-range IP addresses. Two internet-facing web servers are segregated into a DMZ.
Interface Configurations
ISP Link 1 - DSL ISP - Dialer
The PfR-important items are highlighted below. You need to set an accurate figure for the expected bandwidth on the link and set load statistics interval to the lowest setting (30 sec). Also note that both interfaces are designated as 'outside' for NAT.
interface Dialer1
bandwidth 8000
ip address negotiated
ip access-group fwacl in
ip mtu 1492
ip nat outside
ip inspect outside_outCBAC out
ip virtual-reassembly in
encapsulation ppp
ip tcp adjust-mss 1452
load-interval 30
dialer pool 1
dialer-group 1
ppp authentication pap callin
ppp chap refuse
ppp pap sent-username yourUsername password yourPwd
no cdp enable
ISP Link 2 - Wireless ISP - GigE
interface GigabitEthernet0/1
bandwidth 64000
ip address 2.2.2.2 255.255.255.0
ip access-group fwacl in
ip nat outside
ip inspect outside_outCBAC out
ip virtual-reassembly in
load-interval 30
duplex auto
speed auto
no cdp enable
Internal Link - GigE
The link to the LAN is configured as NAT inside.
interface GigabitEthernet1/0
ip address 10.10.10.10 255.255.255.0
ip nat inside
ip virtual-reassembly in
load-interval 30
Routing Configuration
Routing for this scenario is very simple. Just 2 static default routes to the next hop on the respective ISP's.
ip route 0.0.0.0 0.0.0.0 1.1.1.1
ip route 0.0.0.0 0.0.0.0 2.2.2.1
NAT Configuration
The item of interest is the 'oer' command on the NAT inside commands. This alleviates a potential issue with unicast reverse-path forwarding. It's discussed in detail
here.
route-map wispnat_routemap permit 1
match ip address nat_acl
match interface GigabitEthernet0/1
route-map dslnat_routemap permit 2
match ip address nat_acl
match interface Dialer1
ip nat inside source route-map dslnat_routemap interface Dialer1 overload oer
ip nat inside source route-map wispnat_routemap interface GigabitEthernet0/1 overload oer
ip nat inside source static tcp 192.168.40.60 80 interface Dialer1 80
ip nat inside source static tcp 192.168.40.60 443 interface Dialer1 443
ip nat inside source static tcp 192.168.40.61 80 interface GigabitEthernet0/1 80
ip nat inside source static tcp 192.168.40.61 443 interface GigabitEthernet0/1 443
PfR Configuration
Loopback Interface + Key Chain
These are used for communication between the Master and Border elements of PfR.
interface Loopback0
ip address 192.168.200.1 255.255.255.0
key chain pfr
key 0
key-string 7 071F275E450C00
PfR Border Router Config
Really simple config for the border component.
pfr border
logging
local Loopback0
master 192.168.200.1 key-chain pfr
PfR Master Router Config
Configuring the Master is easy as well. In fact, just defining the key-chain and the internal+external interfaces is enough to enable basic load-balancing + fail-over. PfR will aggregrate routes on IP address prefixes and balance across those routes across the 2 ISP links. The extra commands below specify to keep the utilization of the two links within 10 percent of each other, use delay as route learning parameter, evaluate policies every 3 minutes, and make delay the top priority for policy.
pfr master
max-range-utilization percent 10
logging
!
border 192.168.200.1 key-chain pfr
interface GigabitEthernet1/0 internal
interface Dialer1 external
interface GigabitEthernet0/1 external
!
learn
delay
periodic 180
resolve delay priority 1 variance 10
Copyright ©1993-2024 Joey E Whelan, All rights reserved.
