Load Balancing and Failover for ISP links

[techjoe.2]

Dear All,

Please find my requirement in the two figures below

Figure 1Figure 2

Brief Synopsis

In Figure A

I have a Router and two ISP links connected to it. The other end of the Router is connected to the LAN via the Switch

In Figure B

I have two Routers with two different ISP links connected to each of the Routers respectively, for the purpose of maximum uptime. The other end of the Router is connected to the LAN via the Switch.

My Requirement

1. I want to configure Load Balancing and Fail over for the two ISP links. As it is apparent from my requirement, when one ISP link goes down users should be able to access the Internet via the other ISP link.

2. I need the solution in both the cases, with a single Router and two Routers connecting to the ISP links

What would be the most ideal and optimal solution, used as per the Industry standards, to achieve this requirement?

Kindly help me with your suggestions

Cheers!

[Seb Rupik]

Hi there,

Take a look at this document:

https://www.cisco.com/c/en/us/support/docs/ip/border-gateway-protocol-bgp/13762-40.html

...it covers the dual-homed and multihomed scenarios you have described.

cheers,

Seb.

[luis_cordova]

Hi @techjoe.2 

In the first scenario, the objective can be achieved with IP SLA, traking the interface connected to the main ISP. In the second scenario, the objective can be achieved through HSRP, traking or interface connected to the main ISP.

Regards

[techjoe.2]

Thanks for the reply,

As you said,

1. If I use IPSLA it would give me the Failover, but what about Load Balancing ?

[Georg Pauwen · Accepted solution]

Hello,

in both scenarios, since you have (and pay for) two links, you might as well use them both.

In the first scenario, you would have two static default routes which automatically load balance all traffic. The IP SLAs track the Internet connections and remove the static routes when the respective link is down; it also clears the NAT translations. 

The configuration would look like this (IP addresses are arbitrary, obviously):

R1

interface GigabitEthernet0/0
description Link to ISP1
ip address 1.1.1.1 255.255.255.252
ip nat outside
!
interface GigabitEthernet0/1
description Link to ISP2
ip address 2.2.2.1 255.255.255.252
ip nat outside
!
interface GigabitEthernet0/2
description LAN
ip address 192.168.1.1 255.255.255.0
ip nat inside
!
track 1 ip sla 1 reachability
track 2 ip sla 2 reachability
!
ip sla 1
icmp-echo 8.8.8.8 source interface GigabitEthernet 0/0
timeout 500
threshold 500
frequency 2
!
ip sla 2
icmp-echo 8.8.8.8 source interface GigabitEthernet 0/1
timeout 500
threshold 500
frequency 2
!
ip sla schedule 1 start-time now life forever
ip sla schedule 2 start-time now life forever
!
ip route 0.0.0.0 0.0.0.0 1.1.1.2
ip route 0.0.0.0 0.0.0.0 2.2.2.2
!
ip nat inside source list 1 interface GigabitEthernet0/0 overload
ip nat inside source list 1 interface GigabitEthernet0/1 overload
!
access-list 1 permit 192.168.1.0 0.0.0.255
!
event manager applet ISP_1_DOWN
event track 1 state down
action 1.0 cli command "enable"
action 2.0 cli command "conf t"
action 3.0 cli command "no ip route 0.0.0.0 0.0.0.0 1.1.1.2
action 4.0 cli command "exit"
action 5.0 cli command "clear ip nat translation *"
action 6.0 cli command "end"
!
event manager applet ISP_1_UP
event track 1 state up
action 1.0 cli command "enable"
action 2.0 cli command "conf t"
action 3.0 cli command "ip route 0.0.0.0 0.0.0.0 1.1.1.2
action 4.0 cli command "exit"
action 5.0 cli command "clear ip nat translation *"
action 6.0 cli command "end"
!
event manager applet ISP_2_DOWN
event track 2 state down
action 1.0 cli command "enable"
action 2.0 cli command "conf t"
action 3.0 cli command "no ip route 0.0.0.0 0.0.0.0 2.2.2.2
action 4.0 cli command "exit"
action 5.0 cli command "clear ip nat translation *"
action 6.0 cli command "end"
!
event manager applet ISP_2_UP
event track 2 state up
action 1.0 cli command "enable"
action 2.0 cli command "conf t"
action 3.0 cli command "ip route 0.0.0.0 0.0.0.0 2.2.2.2
action 4.0 cli command "exit"
action 5.0 cli command "clear ip nat translation *"
action 6.0 cli command "end"




In the second scenario, you could use GLBP to load balance. An IP SLA on each router monitors the ISP link,and if the ISP link is down, it will shut down the GLBP enabled interface as well (and clear the NAT translations). If only the GLBP enabled interface is down, an EEM script will clear the NAT translations.




The configs would look like this (again, IP addressing is arbitrary):




R1




track 1 ip sla 1 reachability
!
ip sla 1
icmp-echo 8.8.8.8 source interface GigabitEthernet 0/1
timeout 500
threshold 500
frequency 2
!
ip sla schedule 1 start-time now life forever
!
interface GigabitEthernet0/0
description GLBP LAN 1
ip address 192.168.1.2 255.255.255.0
ip nat inside
glbp 1 ip 192.168.1.1
glbp 1 timers msec 50 msec 70
glbp 1 priority 110
glbp 1 preempt
!
interface GigabitEthernet0/1
description Link to ISP
ip address 1.1.1.1 255.255.255.252
ip nat outside
!
ip route 0.0.0.0 0.0.0.0 GigabitEthernet0/1
!
ip nat inside source list 1 interface GigabitEthernet0/1 overload
!
access-list 1 permit 192.168.1.0 0.0.0.255
!
event manager applet GLBP_DOWN
event syslog pattern "Active - Init"
action 1.0 cli command "enable"
action 2.0 cli command "clear ip nat translation *"
action 3.0 cli command "end"
!
event manager applet ISP_DOWN
event track 1 state down
action 1.0 cli command "enable"
action 2.0 cli command "conf t"
action 3.0 cli command "interface GigabitEthernet 0/0"
action 4.0 cli command "shut"
action 5.0 cli command "end"
action 6.0 cli command "clear ip nat translation *"
action 7.0 cli command "end"


R2




track 1 ip sla 1 reachability
!
ip sla 1
icmp-echo 8.8.8.8 source interface GigabitEthernet 0/1
timeout 500
threshold 500
frequency 2
!
ip sla schedule 1 start-time now life forever
!
interface GigabitEthernet0/0
description GLBP LAN 2
ip address 192.168.1.3 255.255.255.0
ip nat inside
glbp 1 ip 192.168.1.1
glbp 1 timers msec 50 msec 70
!
interface GigabitEthernet0/1
description Link to ISP
ip address 2.2.2.1 255.255.255.252
ip nat outside
!
ip route 0.0.0.0 0.0.0.0 GigabitEthernet0/1
!
ip nat inside source list 1 interface GigabitEthernet0/1 overload
!
access-list 1 permit 192.168.1.0 0.0.0.255
!
event manager applet GLBP_DOWN
event syslog pattern "Active - Init"
action 1.0 cli command "enable"
action 2.0 cli command "clear ip nat translation *"
action 3.0 cli command "end"
!
event manager applet ISP_DOWN
event track 1 state down
action 1.0 cli command "enable"
action 2.0 cli command "conf t"
action 3.0 cli command "interface GigabitEthernet 0/0"
action 4.0 cli command "shut"
action 5.0 cli command "end"
action 6.0 cli command "clear ip nat translation *"
action 7.0 cli command "end"

[techjoe.2]

Hi Thanks for your reply,

I found an accepted solution in one of the earlier questions pertaining to the same topic, I have attached the  config file.Can you go through it and let me know if it is fine on your perspective?

[Georg Pauwen]

Hello,

that would work as well, the difference is that you need to specify which traffic you want to go where, but in essence, it achieves the same thing...

[Fargham ahsan]

In the first scenario, I have a problem. could you please solve this?

In the first scenario for instance, if track 1 goes down (8.8.8.8 unreachable) then the router removes the

default route

from the router by using the event manager. Is it possible that track 1  becomes up without adding manually

default routes  (IP route 0.0.0.0 0.0.0.0 1.1.1.2)

? Because track1 state up into event manager could not be enabled unless we add

default route

[Fargham ahsan]

Basically, I want to ask you why we are using the event manager for ISP_1_UP. when we have to add a manually

default route

[paul driver]

Hello

The information provided on your topology isnt clear enough to provide a viable solution at this time.Depending on the below will provide a clearer understanding to what options you have for resiliency and load-balancing

What type of wan connection is being hosted - mpls, internet etc...
What make/model are your wan rtrs, l3 switches, software running on them

What routing EGP/IGP routing protocols if any are you running ( bgp,ospf, eigrp) or static
Are you implementing NAT.