topic Re: Dynamic Route Failover in Switching

Dynamic Route Failover

Jesse Hottle — Wed, 06 Mar 2019 05:42:27 GMT

Hello,

I am trying to get our network traffic to dynamically pick the best route out/in in case of a link failure. I have attached a diagram showing our current router links. The majority of the links are connected to the end-point routers using wireless backhaul bridges. We have two connections forming a ring back to our central noc. (DS3, and PTP fiber connections). Can any one help with this?

Re: Dynamic Route Failover

fahad.sheikh — Wed, 12 Mar 2008 15:57:50 GMT

Can you be specific where u want to acheive this.

My suggetion would be you can use HSRP with interface tracking...

Re: Dynamic Route Failover

Jesse Hottle — Wed, 12 Mar 2008 16:11:24 GMT

Hello,

Any of the router links that go dead, is where I need fail over to take place and re-route customer traffic. Example, router E has three Fe100 interfaces. 1 is directly attached to backhaul bridge, 2 is connected to another backhaul bridge going opposite direction, and 3 would be connected a switch, which feeds various access points which are serving customers for internet access. If INT 1 goes down, I need traffic to route out of INT 2, etc.. Same for all the other connected routers and layer 3 3550.

I do not think all my routers support HSRP, and I am not in a position to upgrade IOS at this time. We have a mixture of static routes, and EIGRP as our routing protocol. All connections eventually terminate at our core 7507 (one is a FE100 interface, the other a serial DS3 connection). We are trying to build a ring to ensure as close to 99% uptime as possible. Also, this got thrown in my lap, so I am a little lost on what to do.

Thanks again for the replies...

Re: Dynamic Route Failover

Jesse Hottle — Thu, 13 Mar 2008 14:22:51 GMT

Can anyone assist in the HSRP configuration? My routers all support this, but I am not sure the best why to setup the virtual routers, or more importantly on which ones.

In some examle I have read, the Active and Standby virtual routers are residing on the same physical subnet. Do I have to set the routers in this way?

Any help would be appriciated.

Thanks

Re: Dynamic Route Failover

Jesse Hottle — Sat, 15 Mar 2008 21:43:59 GMT

Hello?

Any sample configurations would be helpful.

Thanks

Re: Dynamic Route Failover

Istvan_Rabai — Sun, 16 Mar 2008 07:09:28 GMT

Hi Jesse,

Here's a sample configuration of an HSRP pair:

Both Fa0/1 interfaces are in subnet 192.168.1.0/24 (the LAN of hosts), through which hosts reach remote subnets.

Router 1 and Router 2 are the default gateways for these hosts in a redundant pair.

Router 1:

conf t

interface Fa0/1

ip address 192.168.1.1 255.255.255.0

no shutdown

standby 1 ip 192.168.1.10

standby 1 priority 200

standby 1 preempt

standby 1 track serial0/1 50

Router 2:

conf t

interface Fa0/1

ip address 192.168.1.2 255.255.255.0

no shutdown

standby 1 ip 192.168.1.10

standby 1 priority 180

standby 1 preempt

standby 1 track serial0/1 50

This is probably one of the simplest configurations for interface tracking, that track the state of interfaces serial0/1. You can track multiple interfaces the same way.

Note that ip addresses, interface numbers and standby group number are just examples. You should use your own values.

This will provide you a redundant configuration, but only one HSRP router will be active at a time. So one router will always be idle.

However, you can configure load balancing as well with a symmetrical configuration for standby group 2.

The configuration I provided you makes Router 1 as active and Router 2 as standby.

This is done by setting the priority of Router 1 to 200, which is higher than the priority value of Router 2 of 180.

When interface s0/1 goes down on the active router, interface tracking will lower the priority of the router by 50 (the configured value in the standby track command), so its priority will be 150.

At this time, the priority of the standby router becomes higher (180 configured) and will take over the active role from router 1. This is configured by the standby preempt command.

If interface s0/1 comes up again, router 1 will take over the active role again.

Here's the load balancing symmetrical config:

Router 1:

conf t

interface Fa0/1

standby 2 ip 192.168.1.20

standby 2 priority 180

standby 2 preempt

standby 2 track serial0/1 50

Router 2:

conf t

interface Fa0/1

standby 2 ip 192.168.1.20

standby 2 priority 200

standby 2 preempt

standby 2 track serial0/1 50

In this config router 2 will be active and router 1 will be standby. The takever mechanism is the same: router 1 will take ober from router 2 if interface s0/1 goes down, and take over back if it goes up again.

You need to configure one half of the host PCs with default gateway address 192.168.1.10, the other half with default gateway address 192.168.1.20.

Cheers:

Istvan

Re: Dynamic Route Failover

Jesse Hottle — Mon, 17 Mar 2008 17:08:23 GMT

Hello Istvan,

I thought I might need to clarify my needs, so I have attached a simpler network diagram. On the attached drawing, I basically need a setup that will allow my network nodes to still route traffic back to our core 7507 router and onto the internet in the event that any of the interface links on routers A, B, or C happen to go down or fail in any way. I am in the process of completing the configuration of EIGRP as our primary routing protocol for route distribution. Behind each router(A,B,or C), I have multiple secondary IP subnets setup serving hundreds of customers.

So if s0/0 fails on Router A, I would need inbound/outbound traffic to route out the interface f0/1 to the next attached router B and so on..

I am not really concerned with load balancing at this time. But redundancy in the event of a link failure is key.

Thanks for any help.

Re: Dynamic Route Failover

Istvan_Rabai — Tue, 18 Mar 2008 21:31:35 GMT

Hi Jesse,

Sorry for the late response. Today I could free an hour to sit behind the NetPro forum.

The config you provided will give you that failover redundancy you need without HSRP.

If s0/1 goes down on router A EIGRP will automatically use the alternate route through fa0/1 if it is available. And every other router will do the same.

HSRP is needed primarily for default gateway redundancy, though it has a failover feature through interface tracking.

For HSRP you need at least 2 routers for the LAN segment or the VLAN where you want to provide gateway redundancy.

This means you would need 2xRouterA, 2xRouteB, 2xRouterC, just to be simple.

Cheers:

Istvan

Re: Dynamic Route Failover

Jesse Hottle — Thu, 27 Mar 2008 14:08:30 GMT

Hello,

Would it be possible to get some config assistance for using OSPF on this network diagram. I believe this is what we are moving over to, and I got no experience with this routing protocol. Plus, we are going to be integrating other "non-cisco" devices.

What is confusing me is the multiple areas and stub networks. Or do I even need multiple areas?

anything would be great.

Re: Dynamic Route Failover

Istvan_Rabai — Thu, 27 Mar 2008 18:03:11 GMT

Hi Jesse,

Moving to OSPF is a good idea in case you integrate non-cisco devices.

The topology you provided in the Redundant_Project_Simple file, is not so big to be worth bothering with multiple areas at the moment.

Configure all interfaces of all routers for area 0.

Later, if the network grows, then you can use this area 0 as your backbone and expand your network in the locations where your 2950 switches are located now.

Or the number of locations may grow as well, then you can revise the configuration depending on the topology changes.

What is exciting: what is in the NET cloud and how will the OSPF connect to this cloud?

Could you provide info on this?

If you need help in the specific OSPF configurations, please tell me and I will try to post some configs here.

Cheers:

Istvan

Re: Dynamic Route Failover

Jesse Hottle — Thu, 27 Mar 2008 18:43:05 GMT

HI, and thanks for the response. The idea behind OSPF is that we are in the process of integrating with another ISP, and they use limited Cisco gear and all OSPF for their routing protocol. I want both network to be consistant. Our core routing will be all Cisco and I hope to integrate EIGRP, OSPF, and BGP (other OSPF network is on a different carrier).

As for the NET cloud, that basically represents the Internet via our upstream provider. Right now we just get our Internet hand off on a 100mb ethernet connection, directly connected to our Core Router (A) on a /30 subnet. We use a default route at the core (i.e. 0.0.0.0 0.0.0.0 x.x.x.x.)

I could use any config help possible. I am very new to OSPF. Keeping everything on Area 0, helps clarify things for me. I was concerned with virtual-links, etc.. and I have not got my lab fully setup, plus I am lacking some test equipment at this time.

Any help would be great, and I can answer all questions as best as possible.

Thank again,

Re: Dynamic Route Failover

Jesse Hottle — Sat, 29 Mar 2008 17:58:43 GMT

Hello?

Re: Dynamic Route Failover

Istvan_Rabai — Sat, 29 Mar 2008 19:54:56 GMT

Hi Jesse,

Sorry for the late response, I do not log in to the NetPro forum every day.

Some simple OSPF config would be for Core router A in the Redundant_Project file for example:

[Router A config, sample values]

interface serial 1/0

description DS3 to Router B 7206

ip address 192.168.1.1 255.255.255.252

interface fastethernet 1/0

description 100Mbps fiber to Router F 7206

ip address 192.168.1.5 255.255.255.252

ip ospf network point-to-point

interface fastethernet 1/1

description 100Mbps to ISP

ip address x.x.x.1 x.x.x.x

no cdp enable [this may be needed for security purposes, the router will not send CDP packets to the ISP]

router ospf 1

log-adjacency-changes

network 192.168.1.1 0.0.0.0 area 0 [this places interface serial 1/0 into area 0]

network 192.168.1.5 0.0.0.0 area 0 [this places interface fastethernet 1/0 into area 0]

default-information originate [this command causes ospf to send a default route to the internal ospf network, so internal routers know how to reach the outside world]

ip route 0.0.0.0 0.0.0.0 x.x.x.2 [default route to the ISP]

Notice, that I do not start the ospf process on interface fastethernet1/1, because there is no need to exchange updates with the ISP router. You will use a default route to reach the Internet. You need to check with the the ISP that they have a route to your edge router (or to your network) so the reverse traffic to your company can be routed.

[Router F config, sample values]

interface fastethernet 1/0

description 100Mbps fiber to router A 7507

ip address 192.168.1.6 255.255.255.252

ip ospf network point-to-point

interface fastethernet 1/1

description 100Mbps to router E 7206

ip address 192.168.2.1 255.255.255.0 [this is a /24 subnet, as there are switches and hosts on this subnet, but its size may be different depending on the number of hosts residing in the subnet]

router ospf 1

log-adjacency-changes

network 192.168.1.6 0.0.0.0 area 0

network 192.168.2.0 0.0.0.255 area 0

The config for the rest of the routers is similar. You just need to adjust the correct ip addresses and masks on every config line.

I hope this will help you with the start.

Please write if you need help with the configuration of the other routers or switches.

Cheers:

Istvan

Re: Dynamic Route Failover

Jesse Hottle — Tue, 01 Apr 2008 14:36:20 GMT

Hello,

Thanks for the response and info. I am going to setup a test lab and play around with this setup. Are there any issues with OSPF and secondary IP addresses on router interfaces?

Thanks again for the tips and info.

Re: Dynamic Route Failover

Istvan_Rabai — Tue, 01 Apr 2008 19:39:17 GMT

Hi Jesse,

As far as I know there are no issues with the secondary IP addresses.

You only need to be aware that OSPF builds up neighbor relationships and sends routing updates using the primary ip address as the source address.

So don't use the secondary ip addresses to build ospf neighbor relationships.

But you can use the secondary ip address as the default gateway address for hosts on the ip subnet of the secondary ip address.

Cheers:

Istvan

Re: Dynamic Route Failover

Jesse Hottle — Fri, 04 Apr 2008 17:30:07 GMT

Hello Istvan,

On the routers running ospf do I still need to add a default route on each router?

Re: Dynamic Route Failover

Istvan_Rabai — Fri, 04 Apr 2008 18:01:07 GMT

Hi Jesse,

By the suggested config Router A should inject a default route into the internal ospf domain.

This is why I put the "default-information originate" command into the ospf config of router A.

So no other default route config is necessary.

Cheers:

Istvan

Re: Dynamic Route Failover

Jesse Hottle — Fri, 04 Apr 2008 18:08:07 GMT

Thanks for the response..

Also, on all the router interfaces that are directly connected to other routers, should I always use the ip ospf network point-to-point command on that specifc interfaces?

Also, on the ospf network configs you have an inteface assigned as 192.168.1.1 and 192.168.1.5, but within the global ospf config you list the adversitzed networks as 192.168.1.1 0.0.0.0 and 192.168.1.5 0.0.0.0 (why are these not 192.168.1.0 0.0.0.3)..

And on the interface that is connection to a switch for end-users you have 192.168.2.1 255.255.255.0, but on the ospf global you have 192.168.2.0 0.0.0.255)?

Just trying to clarify this up some for my own knowledge.

Thanks again,

Re: Dynamic Route Failover

Istvan_Rabai — Sat, 05 Apr 2008 03:02:59 GMT

Hi Jesse,

Your 1st question:

I used to specifiy "ip ospf network point-to-point" on links that are point-to-point.

The link between Router A and Router F is a fiber optic circuit and it is point-to-point (only these 2 routers are on this link).

If you specify the network type for ospf "ip ospf network point-to-point", the 2 routers form a neighbor relationship automatically but without the use of a designated router (DR)and backup designated router (BDR).

DR and BDR are necessary only when you have more than 2 routers on a broadcast link, or a full mesh of connections on a non-broadcast multiaccess link (e.g. frame relay).

Not using a DR and BDR saves memory and processor cycles for the routers.

Your 2nd question:

0.0.0.0 wildcard mask specifies that all bits of the given address need to be compared with the interface addresses.

The implication of this is that only one interface will be included in the ospf process: the one that has the exact 192.168.1.1 address.

192.168.1.0 0.0.0.3 will achieve the same result in this specific configuration, so you can use it as well.

Your 3rd question:

192.168.2.1 255.255.255.0 specifies the ip address of an interface and its subnet mask.

192.168.2.0 0.0.0.255 uses a wildcard mask instead of a subnet mask.

This wildcard mask means this: 00000000.00000000.00000000.11111111

The bits of the address 192.168.2.0 must be compared with the addresses of the interfaces on the router, where 0s are specified in the wildcard mask.

Where 1s are specified, these are "don't care" bits, there is no need for comparison.

The above wildcard means then: only the leftmost 3 octets must be compared. If these bits match, then the interface is selected under the ospf process.

This is not the same as the subnet mask, where the 1s and 0s must be contiguous.

For a wildcard mask there is not a requirement for 0s and 1s to be contiguous You can have a wildcard mask like this:

00000000.00000000.11111101.11111111

(0.0.253.255)

In this case bit 2 of the 3rd octet is 0, all other bits are 1.

This requires the respective bit of that octet to be compared with the interface addresses. All bits with value 1 don't have to be compared. Bit 1s are called "don't care" bits.

Cheers:

Istvan

Re: Dynamic Route Failover

Istvan_Rabai — Sun, 06 Apr 2008 10:49:02 GMT

Hi Jesse,

Although you didn't mention if you will use a private address space within your internal ospf domain, my supposition is that you will use a private address space.

If this is true, then let me make an addition to the configurations I posted for you beforehand:

If you use private addresses in your internal ospf domain, you will need to do NAT address translation. It is configured on Router A the following way ( I post the modified config for Router A here):

[Router A config, sample values]

interface serial 1/0

description DS3 to Router B 7206

ip address 192.168.1.1 255.255.255.252

ip nat inside [part of the NAT config]

interface fastethernet 1/0

description 100Mbps fiber to Router F 7206

ip address 192.168.1.5 255.255.255.252

ip ospf network point-to-point

ip nat inside [part of the NAT config]

interface fastethernet 1/1

description 100Mbps to ISP

ip address x.x.x.1 x.x.x.x

ip nat outside [part of the NAT config]

no cdp enable [this may be needed for security purposes, the router will not send CDP packets to the ISP]

router ospf 1

log-adjacency-changes

network 192.168.1.1 0.0.0.0 area 0 [this places interface serial 1/0 into area 0]

network 192.168.1.5 0.0.0.0 area 0 [this places interface fastethernet 1/0 into area 0]

default-information originate [this command causes ospf to send a default route to the internal ospf network, so internal routers know how to reach the outside world]

ip route 0.0.0.0 0.0.0.0 x.x.x.2 [default route to the ISP]

ip nat inside source list 1 interface fastethernet1/1 overload [part of the NAT config]

access-list 1 permit 192.168.0.0 0.0.255.255 [part of the NAT config]

I hope this will give you an additional help in your configuration work.

Cheers:

Istvan