Rule #1 – Just because Host 1 can get to Host 2, does NOT mean that Host 2 can get back to Host 1!
I can’t tell you how many times I’ve seen this out in the field. Here is a prime example.
This is quite a simply common topology. OfficeA and OfficeB have a WAN connection running between them. RouterA and RouterB are under control of the ISP and are running OSPF. RouterC is a customer-owned router, and so doesn’t run any OSPF with RouterA or RouterB.
OfficeB has an internet connection, and RouterB is injecting a default route to OfficeA via OSPF.
RouterB has a default route to RouterC. So let’s think about traffic flow now. A host connected to RouterA needs to send traffic to the internet. It will send it’s traffic to it’s default gateway, RouterA. RouterA has a default route injected into OSPF from RouterB and so sends traffic to RouterB.
RouterB has a default route and hence sends that traffic out to RouterC. Which then goes out to the internet.
Traffic then flows back from the internet to RouterC. The return address will be an IP that belongs in RouterA and RouterB’s routing table, however RouterC has no knowledge of that subnet (as it’s not participating in OSPF). RouterC will just use it’s default route and send that packet back out to the internet. Eventually the TTL will kill that packet.
This can be fixed by putting a static route on RouterC to let it know that RouterA’s ip range needs to be sent off to RouterB instead.
A similar thing will happen if we add a server to SwitchA. That server’s default gateway will most likely be RouterC. If a host in OfficeA send a PING to that server, that server will then send traffic off to RouterC. If RouterC does not have the static route added above, it’ll send it out to the internet.
I’m well aware that the design in the picture is pretty bad, but I used it to illustrate a point. That point being that just because router’s know how to get from A to B, it does NOT mean they know how to route that traffic back. Make sure you understand this!
The diagram is the same as my last VPN Lab. Also it uses my MPLs topology found over here: http://mellowd.co.uk/ccie/?p=522
This is the topology for this lab (click for a bigger image):
- Customer1 and Customer 2 both have MPLS vpn’s through the ISP core.
- Customer1 is using OSPF and Customer2 is using EIGRP
- Customers should have no access to each others networks
- Customers should be able to reach all their sites from all their sites
- The ISP wants to monitor the CPE routers via their monitoring server. Create another loopback on each CPE router and give them all a /32 loopback in the 172.16.1.1/24 range – i.e. 172.16.1.1/32 for CPE1, 172.16.1.2/32 for CPE2 and so on
- Ensure the monitoring router can get to all these /32 routes (and ONLY these /32 routes) – It should not know about any customer routes – CPE routers should only see their OWN loopbacks in the routing table
- Now enable CPE3 and CPE6 to see each others subnets. All other CPE routers should see no change in their routing tables
This lab will test a Central Services MPLS VPN.
The diagram is the same as my last VPN Lab. Also it uses my MPLs topology found over here: http://mellowd.co.uk/ccie/?p=522
This is the topology for this lab (click for a bigger image):
- Customer1 and Customer 2 both have MPLS vpn’s through the ISP core.
- Customer1 is using OSPF and Customer2 is using EIGRP
- Customers should have no access to each others networks
- Customers should be able to reach all their sites from all their sites
- The ISP is now providing a mail relay for it’s customers to use. Ensure that all customers can get to the 10.200.1.1/24 subnet through their vpn’s, but they must still be seperated from each other.
This VPN lab will test intranet and extranet MPLS VPN’s.
The diagram is the same as my last VPN Lab. Also it uses my MPLs topology found over here: http://mellowd.co.uk/ccie/?p=522
This is the lab topology again:
- CPE1 and CPE5 belong to Customer1
- CPE2 and CPE6 belong to Customer2
- Both customers are running OSPF as their IGP’s
- The loopbacks as shown in the topology must be advertised into OSPF. Cutomer1 should be able to ping all loopbacks in their networks and Customer2 should be able to ping everything in theirs.
- Both customers are now running a project together, and need 2 of their offices connected. CPE1 from Customer1 should be able to communicate with CPE6 from Customer2 and vice-versa
- It’s essential that CPE2 and CPE5 are NOT able to get to all loopbacks. ONLY CPE1 and CPE6 should be able to communicate with each other. This new configuration should not break the previous VPN’s in place
- Do this without using any ACL’s, Prefix-lists, Route-maps or the like
Hopefully this will be my final tweak. This time I’ve added base configs to the CPE devices. It just gives them a hostname and ensures there is no timeout. This prevents you from having to keep logging back in.
Image-wise, it’s the same. Click for the larger image:
This is the .net file contents:
#MPLS 1.0 Topology created by Darren O'Connor 22/02/10 #MPLS 1.1 created 23/02/10 #MPLS 1.2 created 24/02/10 #www.mellowd.co.uk/ccie #Feel free to use and change as you see fit. However if you do use please leave my details here at the top [localhost:7200] workingdir = /data/dynamips/working [[3640]] image = /data/dynamips/IOS_Images/3640/c3640-js-mz.124-25c.UNCOMPRESSED.bin ram = 128 disk0 = 0 disk1 = 0 mmap = true ghostios = true ########################### # # # Mpls Topology 1.2 # # # ########################### [[Router CR1]] model = 3640 console = 2001 autostart = true idlepc = 0x605105b8 slot0 = NM-1FE-TX slot1 = NM-4T slot2 = NM-1FE-TX s1/0 = AR1 s1/0 s1/2 = AR3 s1/2 Fa0/0 = CR3 Fa0/0 Fa2/0 = CR2 Fa2/0 cnfg = /data/dynamips/Topology/Topology_Config/mpls/CR1.cfg [[Router CR2]] model = 3640 console = 2002 autostart = true idlepc = 0x605105b8 slot0 = NM-1FE-TX slot1 = NM-4T slot2 = NM-1FE-TX s1/0 = AR2 s1/0 s1/2 = AR1 s1/2 Fa0/0 = CR4 Fa0/0 cnfg = /data/dynamips/Topology/Topology_Config/mpls/CR2.cfg [[Router CR3]] model = 3640 console = 2003 autostart = true idlepc = 0x605105b8 slot0 = NM-1FE-TX slot1 = NM-4T slot2 = NM-1FE-TX Fa2/0 = CR4 Fa2/0 s1/0 = AR3 s1/0 s1/1 = GR1 s1/1 s1/2 = AR4 s1/2 cnfg = /data/dynamips/Topology/Topology_Config/mpls/CR3.cfg [[Router CR4]] model = 3640 console = 2004 autostart = true idlepc = 0x605105b8 slot0 = NM-1FE-TX slot1 = NM-4T slot2 = NM-1FE-TX s1/0 = AR4 s1/0 s1/2 = AR2 s1/2 cnfg = /data/dynamips/Topology/Topology_Config/mpls/CR4.cfg [[Router AR1]] model = 3640 console = 2005 autostart = true idlepc = 0x605105b8 slot0 = NM-1FE-TX slot1 = NM-4T slot2 = NM-1FE-TX Fa0/0 = CPE1 Fa0/0 Fa2/0 = CPE2 Fa0/0 cnfg = /data/dynamips/Topology/Topology_Config/mpls/AR1.cfg [[Router AR2]] model = 3640 console = 2006 autostart = true idlepc = 0x605105b8 slot0 = NM-1FE-TX slot1 = NM-4T slot2 = NM-1FE-TX Fa0/0 = CPE4 Fa0/0 Fa2/0 = CPE3 Fa0/0 cnfg = /data/dynamips/Topology/Topology_Config/mpls/AR2.cfg [[Router AR3]] model = 3640 console = 2007 autostart = true idlepc = 0x605105b8 slot0 = NM-1FE-TX slot1 = NM-4T slot2 = NM-1FE-TX Fa0/0 = CPE5 Fa0/0 Fa2/0 = CPE6 Fa0/0 cnfg = /data/dynamips/Topology/Topology_Config/mpls/AR3.cfg [[Router AR4]] model = 3640 console = 2008 autostart = true idlepc = 0x605105b8 slot0 = NM-1FE-TX slot1 = NM-4T slot2 = NM-1FE-TX Fa0/0 = CPE8 Fa0/0 Fa2/0 = CPE7 Fa0/0 cnfg = /data/dynamips/Topology/Topology_Config/mpls/AR4.cfg [[Router CPE1]] model = 3640 console = 2009 autostart = false idlepc = 0x605105b8 slot0 = NM-1FE-TX cnfg = /data/dynamips/Topology/Topology_Config/mpls/CPE1.cfg [[Router CPE2]] model = 3640 console = 2010 autostart = false idlepc = 0x605105b8 slot0 = NM-1FE-TX cnfg = /data/dynamips/Topology/Topology_Config/mpls/CPE2.cfg [[Router CPE3]] model = 3640 console = 2011 autostart = false idlepc = 0x605105b8 slot0 = NM-1FE-TX cnfg = /data/dynamips/Topology/Topology_Config/mpls/CPE3.cfg [[Router CPE4]] model = 3640 console = 2012 autostart = false idlepc = 0x605105b8 slot0 = NM-1FE-TX cnfg = /data/dynamips/Topology/Topology_Config/mpls/CPE4.cfg [[Router CPE5]] model = 3640 console = 2013 autostart = false idlepc = 0x605105b8 slot0 = NM-1FE-TX cnfg = /data/dynamips/Topology/Topology_Config/mpls/CPE5.cfg [[Router CPE6]] model = 3640 console = 2014 autostart = false idlepc = 0x605105b8 slot0 = NM-1FE-TX cnfg = /data/dynamips/Topology/Topology_Config/mpls/CPE6.cfg [[Router CPE7]] model = 3640 console = 2021 autostart = false idlepc = 0x605105b8 slot0 = NM-1FE-TX cnfg = /data/dynamips/Topology/Topology_Config/mpls/CPE7.cfg [[Router CPE8]] model = 3640 console = 2022 autostart = false idlepc = 0x605105b8 slot0 = NM-1FE-TX cnfg = /data/dynamips/Topology/Topology_Config/mpls/CPE8.cfg [[Router GR1]] model = 3640 console = 2023 autostart = true idlepc = 0x605105b8 slot0 = NM-1FE-TX slot1 = NM-4T Fa0/0 = ISP2 Fa0/0 cnfg = /data/dynamips/Topology/Topology_Config/mpls/GR1.cfg [[Router ISP2]] model = 3640 console = 2024 autostart = false idlepc = 0x605105b8 slot0 = NM-1FE-TX cnfg = /data/dynamips/Topology/Topology_Config/mpls/ISP2.cfg
And here are the updated config files: http://mellowd.co.uk/ccie/wp-content/uploads/2010/02/mpls.tar2.gz
Topology used is over here: http://mellowd.co.uk/ccie/?p=243
BGP Lab 12:
- AS7, AS9 and AS11 are all customers of ISP1
- AS7 has it’s own address space – 77.48.16.0/24 advertised via a loopback
- ISP1 owns the address space 180.16.0.0/16
- AS9 has been assigned 180.16.9.0/24 from ISP1 – insert via loopback
- AS11 has been assigned 180.16.11.0/24 from ISP1 – insert via loopback
- Ensure that AS7′s address space is advertised to AS9 and AS11
- ISP1 needs to advertise the entire 180.16.0.0/16 range and not the more specific routes. Ensure AS7 sees only 180.16.0.0/16 HOWEVER it must still know that some routes have come from AS9 and AS11
- On AS9, configure an attribute so that ISP1 does not advertise the more specific 180.16.9.0/24 address to anyone.
- You should notice that ISP1 is now not advertising the aggregate because it has inherited the no-export community from above
- Now on ISP1, ensure that the community is changed so that the aggregate can be advertised again
Click on the thumbnail for the full size topology:
Topology used is over here: http://mellowd.co.uk/ccie/?p=243
BGP Lab 11:
- All routers are peered via BGP
- Router9 has the network 24.83.176.1/24 attached via a loopback
- Router2 has the network 24.83.177.1/24 attached via a loopback
- All networks MUST be inserted into the BGP process
- Now ensure that Router8 and Router1 see the full aggregate of 24.83.176/23 advertised. More specific routes MUST be supressed. i.e. Router1 and Router8 should have the aggregate ONLY – Do this WITHOUT removing any of the networks from the BGP process
- Now change the configuration so that Router1 and Router8 get the aggregate as well as the more specific routes, however using a community tag (on Router2), ensure that Router1 does NOT advertise the more specific routes to Router6.
- Router6 should still get the aggregate route
- Check to make sure Router1 has all the routes and Router6 ONLY has the aggregate route
Click on the thumbnail for the full topology:
Topology used is over here: http://mellowd.co.uk/ccie/?p=243
BGP Lab 10:
- CompanyA is a customer of ISP1
- CompanyA is peered with CompanyB which is NOT a customer of ISP1
- ISP1 advertises the loopbacks of both Router8 and Router9, however wants to ensure that only it’s own customers know about 8.8.8.8
- ISP1 does not care that all routers know about 9.9.9.9
- ISP1 does not trust CustomerA to put the right measure in place, so you need to do it from the ISP1 side.
- In other words, make sure that CompanyA knows about 8.8.8.8 but force it not to advertise that route any further
Click on the thumbnail for the full topology:
Topology used is over here: http://mellowd.co.uk/ccie/?p=243
BGP Lab 9:
- ISP1 is running OSPF internally so that all loopbacks are accessible
- Router1 has the network 172.20.1.0/24 attached to it (via a loopback)
- Router8 has the network 172.20.8.0/24 attached to it (via a loopback)
- Ensure both these networks are advertised by both Router1 and Router8
- ISP1 contains the entire 172.20.0.0/16 network. Ensure this aggregate is always advertised out, no matter the condition of the more granular networks
- Using MED, ensure traffic from Router10 to 172.20.1.0/24 goes via Router2 and traffic to 172.20.8.0/24 goes via Router9
- Ensure the MED comes from the OSPF metric itself
Click on the thumbnail for the full topology:
Topology used is over here: http://mellowd.co.uk/ccie/?p=243
BGP Lab 8:
- Address as normal in the topology – Add the loopback of 99.99.99.99 and 22.22.22.22 to Router’s 9 and 2 respectively
- All routers are peered via BGP with OSPF running as well
- Use a filter on AS500 to ensure it is non-transit
- Company1 now wants to prepend it’s AS number 3 times for any route sent off to Customer2
- Allow Customer3 to transit through ISP1
- Ensure Customer3′s Private-AS number is stripped off before advertising it out
- Allow Company1 and Company2 to get to Customer3
Click on the thumbnail for the full topology:
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