Layer 2/3 Load-Balancing Question

[Plum_TreeS]

Hey Guys/Gals,

I have a network that has a 4G Modem, Satellite Communication device, and an Interoperability connection. These three devices should send in a precedence of 4G, SATCOM, Interop. To achieve this I set 3 floating routes each of which increment by 1 (i.e. ip route 0.0.0.0 0.0.0.0 G1/0/1, ip route 0.0.0.0 0.0.0.0 G1/0/2 2) which is in working order. Now the part that I have been racking my brain on is load-balancing. This seems simple enough however the 4G Modem, SATCOM, and Interop are all separate manufactured devices so something like HSRP wouldn't work if I'm thinking right. The need for load-balancing is due to the possibility of signal degradation of 4G or SATCOM in which I would prefer the other device pick up the slack in sending. Being that 3 different connections provide WAN services, I'd also like for the passed DHCP default-gateway (hosted on Layer3Switch) be one seamless address or if unachievable, a way for the default-gateway to change transparently for the end user. Furthermore, is there a protocol that can cluster three ports together on one end and provide a single address for the users?

Apologies in advance if this is poorly explained. Just wondering the solution! Thanks in advance.

[balaji.bandi]

You need to have device which can make decision and failver.

1. you should do Policbased routing means, some traffic to Link 1 and some traffic to Link2

2. If the Link1 Fails move the traffic to Link 2, vice version

so steps

PBR Policbased routing

IP SLA to track this and make a decision

NAT

[Plum_TreeS]

Balaji, thank you very much for a place to start!

 Thank you,

 Jeremy

[Georg Pauwen]

Hello,

GLBP (Gateway Load Balancing Protocol) might be a solution, as that also has load balancing capabilities. If possible, post the running configuration of your router...

[Giuseppe Larosa]

Hello @Plum_TreeS ,

>> his seems simple enough however the 4G Modem, SATCOM, and Interop are all separate manufactured devices so something like HSRP wouldn't work if I'm thinking right. The need for load-balancing is due to the possibility of signal degradation of 4G or SATCOM in which I would prefer the other device pick up the slack in sending. Being that 3 different connections provide WAN services,

>> I'd also like for the passed DHCP default-gateway (hosted on Layer3Switch) be one seamless address or if unachievable, a way for the default-gateway to change transparently for the end user. Furthermore, is there a protocol that can cluster three ports together on one end and provide a single address for the users?

Regarding the second question you would need a router to be placed on the path between the internal L3 switch and the three different external WAN devices and then using NAT on the router.

The router is needed because your L3 switch is likely not able to perfomr NAT.

In this way you can use your own internal IP subnet(s)  and the router will be the default gateway for the L3 switch and it will be in charge of performing source based NAT in different ways according to which WAN exit link is chosen.

In a scenario like yours is easier to implement a strict hierarchy on your WAN links rather then performing load balancing combining it with IP SLA.

However, if you want in normal conditions to divert some traffic flows on the WAN2 SATCOM you can do it using a route-map and PBR but the route-map is applied inbound on the LAN interface between the router and L3 switch and it should set the outgoing interface and /or the the ip next-hop to the WAN2 IP address next-hop.

For NAT the best way to deal with multiple exit interfaces is to use additional route-maps that check the outgoing interface in addition to use a match address that invokes an extended ACL.

Access-list    120 remark for PBR

access-list permit ip  10.1010.0 0.0.0.255 any

route-map PBR permit 10

match address 120

set ip next-hop <SATCOM IP address>

set ip next-hop verify-availabilty

interface gi0/0/0

desc link between router and internal L3 switch

ip policy route-map PBR

ip nat inside

Then you have three interfaces connecting to the three WAN interfaces

gi0/0/1 to 4G MODEM

gi0/0/2 to SATCOM

gi0/0/3 to interoperability link

address-list 125 remark ACL for NAT 4G

address-list 125 permit ip 10.10.10.0 0.0.0.255 any

if you want to have separate counters to see hits it is better to use othe ACLs

address-list 126 remark ACL for NAT SATCOM

address-list 126 permit ip 10.10.10.0 0.0.0.255 any

address-list 127 remark ACL for NAT SATCOM

address-list 127 permit ip 10.10.10.0 0.0.0.255 any

! now we create the three route-maps used for interface aware NAT

! in this route-maps the match interface checks the outgoing inteface and it is a match if traffic is going to exit

! from the specified interface

route-map NAT-4G permit 10

match address 125

match interface gi0/0/1

route-map NAT-SAT permit 10

match address 126

match interface gi0/0/2

route-map NAT-WAN3 permit 10

match address 126

match interface gi0/0/3

int gi0/0/1

ip nat outside

!

int gi0/0/2

ip nat outside

!

int gi0/0/3

ip nat outside

finally in global config three NAT statements

ip nat inside source route-map NAT-4G interface gi0/0/1 overload

ip nat inside source route-map NAT-SAT interface gi0/0/2 overload

ip nat inside source route-map NAT-WAN3 interface gi0/0/1 overload

You still need floating default static routes and IP SLA

Hope to help

Giuseppe

[Plum_TreeS]

Giuseppe, thank you very much. I wasn’t given enough time to implement but thank you so much for the in depth analysis on PBR. I will surely be using this as reference when configuring in the future. 

Thank you,

 Jeremy

[paul driver · Accepted solution]

Hello

---

@Plum_TreeS wrote:

The need for load-balancing is due to the possibility of signal degradation of 4G or SATCOM in which I would prefer the other device pick up the slack in sending

---

Based on what you have stated above policy-based routing (PBR) wouldn’t be applicable , PBR would detect connectivity loss with the help of IPSA monitoring however it wouldn’t detect degradation of signal/throughput or delay. To load balancing on these parameters you would require the rtr to support a feature called Performance or Optimized Edge Routing ( PFR/OER)

So when PFR/OER is applied on you rtr(s) which has connection to dual ISPs it will load share by pushing traffic to the alternative ISP as/ when it detects congestion/delay or even loss over your primary ISP connection

PFR/OER is designed to LB your traffic between dual ISPs based on these parameters as such so to select the best path, at any given time

[Plum_TreeS]

Thank you Paul, I believe it is a device capability/function issue I am running into unfortunately. I was given about 2 days to learn and configure so I wasn’t able to implement much but have learned a lot from these posts!

 Thank you,

 Jeremy