static routing

[jack samuel]

Dears,

Please find the attached topology

i have a general question,

A laptop is always reaching the server by preferred route by RTR3 , when the preferred route fails switches send via HSRP VIP IP address 192.168.10.1/24  to RTR4  to route to the server via MPLS  and for  the return traffic when it want to reach to laptop RTR 4 routes via VIP IP address on switches 172.24.1.1/24  does this routing will create a problem for the data path , and is this is called a asymmetric routing??

In summary :

3 subnets will be used 192.168.10.0/24,,172.24.1.0/24, and 192.168.11.0/24

RTR1 pointing to VIP on switches (192.168.11.0/24), switches points to RTR3

If RTR3 fails  switches by IP SLA routes to VIP of the routers (assume RTR4 active 192.168.10.1)

For Return traffic from Server RTR4 throws a packet on active VIP of switches. (172.24.1.1)

Please correct me if the design is wrong

thanks

[Julio E. Moisa]

Hi

Could you please attach the topology?

Thank you in advance. 

[jack samuel]

Dear Julio,

Already attached

[Julio E. Moisa]

Hi

Thank you so much Jack, yes you have asymmetric traffic, what routing protocol have you using between RTR2 and RTR4? have you verified the metrics between these routers, if you are using OSPF the cost should be verified. Something on RTR4 is preferring the network 192.168.10.0/24 as next hop. 

Could you please share the show ip route for the Laptop's IP on RTR4? or the configuration of RTR2 and RTR4

Thank you in advance. 

:-)

[jack samuel]

Dear Julio,

I have changed the topology actually i did a mistake in previous topology,

Assume Laptop is an internal subnet on the core switch, and all SVI of the core has been advertise in BGP , i have BGP peering between the RTR2 ,RTR4,and core switches.

RTR3 has a static route to switches to reach internal subnets

RTR2 and RTR4 GIG0/1 is in subnet 192.168.10.0/24 and both switches have a SVI IP address from these subnet so that they can point to the VIP of the routers to route traffic to server incase the link on RTR3 fails.

The return traffic from the server will reach to RTR4 , then BGP will take care to route to internal network becz it has BGP peering with core switch and on core switch we have advertise the subnet.

If incase anybody sitting on RTR2 or RTR4 and trying to ping the server then they shld hit the VIP on the switches ( 172.24.1.0/24) to route to the server and incase the link fails on  RTR3 it will go through MPLS line by ISP.

so pls assume if i have static route to laptop pointing on RTR2 & RTR4 to VIP 172.24.1.1 of switches does that asymmetric will cause issue.

Please correct me if i am wrong. 

[Julio E. Moisa]

Thank you Jack,

a static route will be preferred than an eBGP route, Please correct me, RTR2 and RTR4 are connected to the MPLS through eBGP, is that correct?  Your currently have an iBGP between RTR1, RTR2 and RTR4. 

You can use static route and it will work but is not the best solution, if you have eBGP between RTR2 to MPLS, and RTR4 to MPLS you could use BGP attributes like local-preference to prefer a path and AS-Path to avoid asymmetric traffic. 

:-)

[jack samuel]

Dear Julio,

a static route will be preferred than an eBGP route

yes, i will be tracking a route to server on routers pointing to switches VIP if incase the preferred route fails on RTR3 it will use the ISP MPLS link through BGP which it is receiving from WAN

Please correct me, RTR2 and RTR4 are connected to the MPLS through eBGP, is that correct?

yes

if you have eBGP between RTR2 to MPLS, and RTR4 to MPLS you could use BGP attributes like local-preference to prefer a path and AS-Path to avoid asymmetric traffic.

yes it is in place this link i will use only on failure of link RTR3

Please correct me if i m wrong how it is an asymmetric routing ??

for Example  take 2 routers with 2 ethernet ports point-to-point connection as per the diagram,From RTR1 if i want to route to 172.24.X.X i will point on gig0/0 and RTR2 if he wants to route to 192.168.X.X he will point the exit path from gig0/1.

Routers are not stateful they can route from anywhere from their routing table

Thanks

[jack samuel]

Dears,

Anybody can help for the above design

thanks

[Joseph W. Doherty]

To accomplish symmetric routing?

There's often nothing wrong with asymmetrical routing unless you're dealing with devices that need to see the conversation's traffic in both directions or you're mixing routers and switches and with their typical default timers creating unicast flooding.

[jack samuel]

Dear experts (Julio,Joseph)

so  joseph you are mentioning that asymmetric routing is my design will not cause any issue, also can u elaborate more on your paragraph

unless you're dealing with devices that need to see the conversation's traffic in both directions or you're mixing routers and switches and with their typical default timers creating unicast flooding

Dear Julio,

Can you give me the solution for this scenario if you are saying that asymmetric routing may cause an issue

Thanks

[Julio E. Moisa]

Hi Jack,

I have had cases where the asymmetric traffic generate problems because there are different routing protocols but in this case we need to verify the behavior, is possible to know the configuration of both routers?

[Joseph W. Doherty]

Examples of devices that often depend on seeing packets in both directions are firewalls and NAT.

However, end hosts normally only concern themselves with the packets being delivered to them.  They don't generally care what the path was from sender to receiver beyond often being impacted if a sequence of packets arrives out-of-order.

[Julio E. Moisa]

Hi Jack,

Apologies for the late response, the asymmetric traffic will send the packet through a link and the remote router will response from the second link, so that could generate inconveniences.