Multipath WAN

[battanc]

I have a DataCenter and some Branch-Offices connected in MPLS.
For one of these, very critical, I have to guarantee continuity of connection to the Data Center, also in case of problems on the MPLS.
So I have to add one or two alternative routes.
The question is: how do I manage at best the automatic route selection: SLA-TRACK or Dynamic routing OSPF / EIGRP
In the first case, I wonder if SLA-TRACK can handle multiple paths.
In the second case, I wonder if a dynamic routing can be transparent to the provider, because I doubt that he agrees to adapt his configuration to mine.

[Georg Pauwen]

Hello,

dynamic routing protocols are not a good idea, most ISPs support only BGP anyway, so you are better off using static routes. SLA can track multiple routes, you can build in whatever dependency you need (e.g. route 3 gets activated when BOTH route 1 and route 2 are uanavailable, or when ONLY one of the two is unavailable). Typically you would use a boolean operator to configure this dependency.

[Georg Pauwen]

Here are two configuration examples, one for a router with two (primary and backup) links, the second for a router with three links. In the second example, the boolean operator in the track list will make sure that when one link is down, the next one will be used, in sequence.

It is recommended to add the EEM script as stated, in order to make sure that the NAT entries are immediately cleared.

Example 1:

interface FastEthernet0/0
description ISP Primary
ip address 100.100.100.1 255.255.255.252
!
interface FastEthernet0/1
description ISP Backup
ip address 200.200.200.1 255.255.255.252
!
ip sla 1
icmp-echo 8.8.8.8 source-interface FastEthernet0/0
timeout 1000
threshold 2
frequency 3
!
ip sla schedule 1 life forever start-time now
!
track 1 ip sla 1 reachability
!
ip route 0.0.0.0 0.0.0.0 100.100.100.2 track 1
ip route 0.0.0.0 0.0.0.0 200.200.200.2 10
!
event manager applet CLEAR_NAT
event track 1 state any
action 1.0 cli command “enable”
action 2.0 cli command “clear ip nat translation *”
action 3.0 cli command "end"

------------------

Example 2:

track 1 ip sla 1 reachability
!
track 2 ip sla 2 reachability
!
track 3 list boolean or
object 1
object 2
!
interface FastEthernet0/0
description ISP Primary
ip address 100.100.100.1 255.255.255.252
duplex auto
speed auto
media-type rj45
!
interface FastEthernet0/1
description ISP Secondary
ip address 150.150.150.1 255.255.255.252
duplex auto
speed auto
media-type rj45
!
interface FastEthernet0/2
ip address 200.200.200.1 255.255.255.252
description ISP Terciary
duplex auto
speed auto
media-type rj45
!
ip route 0.0.0.0 0.0.0.0 100.100.100.2 track 1
ip route 0.0.0.0 0.0.0.0 150.150.150.2 100 track 2
ip route 0.0.0.0 0.0.0.0 200.200.2000.2 200
!
ip sla 1
icmp-echo 8.8.8.8 source-interface FastEthernet0/0
threshold 1000
timeout 3000
frequency 3
ip sla schedule 1 life forever start-time now
ip sla 2
icmp-echo 8.8.8.8 source-interface FastEthernet0/1
threshold 1000
timeout 3000
frequency 3
ip sla schedule 2 life forever start-time now
!
event manager applet CLEAR_NAT
event track 3 state any
action 1.0 cli command “enable”
action 2.0 cli command “clear ip nat translation *”
action 3.0 cli command "end"