topic Hi Jon, in Switching

ASR9001 routing question

tinhnho123 — Fri, 08 Mar 2019 12:50:45 GMT

Hello,

I'm given a subnet 73.24.24.240/28 from my ISP. Everything was working with my old edge router. I was trying to replace my old edge router with ASR9001 and I believe I'm having issue with routing. My ASR router is connected to ISP router and my layer3 switch (the attachment is my topology).

On the ASR router, I divided the subnet 73.24.24.240/28 into small subnets:
73.24.24.240/29

73.24.24.248/29

Below are configurations of the ASR:

interface GigabitEthernet0/0/0/0
description to Internet
ipv4 address 73.24.24.241 255.255.255.248
speed 1000
negotiation auto
!

interface GigabitEthernet0/0/0/1
description to Layer3 switch
ipv4 address 73.24.24.249 255.255.255.248
speed 1000
negotiation auto

router static
address-family ipv4 unicast
0.0.0.0/0 73.24.24.245 14
!

Note: The IP address 73.24.24.245 is the ISP router's G0/1 interface (or my ASR next hop).

router ospf 1
log adjacency changesrouter-id 73.24.24.241
nsf cisco
auto-cost reference-bandwidth 1000
redistribute static metric-type 1
area 1
nssa default-information-originate metric-type 1
interface GigabitEthernet0/0/0/1

Below is the Layer3 switch setup:

interface vlan 2
ip address 73.24.24.250 255.255.255.248

ip default-gateway 73.24.24.249

interface g1/1/1
switchport
switchport access vlan 2
switchport mode access
no shut

From the ASR, I can ping 8.8.8.8, 73.24.24.245 and 73.24.24.250 (layer3 switch).

From Layer3 switch, I can ping both interfaces of ASR g0/0/0/0 and g0/0/0/1 IP addresses, but can not ping 73.24.24.245 and 8.8.8.8.

Do you guys have any ideas why my Layer3 switch can not ping 73.24.24.245 and 8.8.8.8 and others? If it's unclear, please feel free to let me know.

Thanks.

"ip default-gateway 73.24.24

Iulian Vaideanu — Sun, 06 Mar 2016 14:20:57 GMT

"ip default-gateway 73.24.24.248" doesn't look right (should be .249)

sorry for the typo. it's 73

tinhnho123 — Sun, 06 Mar 2016 15:33:38 GMT

sorry for the typo. it's 73.24.24.249.

You said that you divided

Iulian Vaideanu — Sun, 06 Mar 2016 19:09:03 GMT

You said that you divided your subnet when you migrated to the ASR - it could happen that the ISP's router still has /28 as netmask for its .245 interface towards you, and when it tries to reply to .250 (your Layer3 switch) it expects to find it "locally" (on the same network) and not behind another router (your ASR).

Hello,

tinhnho123 — Thu, 10 Mar 2016 20:01:25 GMT

Hello,

I think you're right as the ISP still has /28 as netmask.

Since that way didn't work, I've changed the ASR's g0/0/0/1 to have private ip 192.168.0.1/24

interface GigabitEthernet0/0/0/0
description to Internet
ipv4 address 73.24.24.241 255.255.255.248
speed 1000
negotiation auto
!

interface GigabitEthernet0/0/0/1
description to Layer3 switch
ipv4 address 192.168.0.1 255.255.255.0
speed 1000
negotiation auto

router static
address-family ipv4 unicast
0.0.0.0/0 73.24.24.245 14
!

router ospf 1

log adjacency changesrouter-id 73.24.24.241
nsf cisco
auto-cost reference-bandwidth 1000
redistribute static metric-type 1
area 1
nssa default-information-originate metric-type 1
interface GigabitEthernet0/0/0/1

My Layer 3 switch now has:

interface vlan 2
ip address 192.168.0.2 255.255.255.0

ip default-gateway 192.168.0.1

interface g1/1/1
switchport
switchport access vlan 2
switchport mode access
no shut

I can ping the ASR's g0/0/0/0 and g0/0/0/1 interfaces from my switch but can't ping 8.8.8.8 or any other public addresses. Any ideas? Thanks.

You need to setup NAT because

Jon Marshall — Thu, 10 Mar 2016 23:58:15 GMT

You need to setup NAT because you are using private IPs and they need translating to one of your public IPs, either the interface IP or one of the other IPs in that subnet.

Jon

Hi Jon,

tinhnho123 — Fri, 11 Mar 2016 00:10:05 GMT

Hi Jon,

I had NAT setup on my old router but this ASR 9001 does not have NAT commands that I can use in this case. Are there any other ways around without setup NAT?

Thanks.

Your original solution should

Jon Marshall — Fri, 11 Mar 2016 00:55:07 GMT

Your original solution should work as long as the interface on your ASR that connects to the ISP has proxy arp enabled.

The ISP will simply send an arp for all IPs and your ASR should respond for the IPs on the inside with the mac address of it's outside interface.

It may be the ISP router has some incorrect arp entries from before you switched over.

Jon

Hello Jon,

tinhnho123 — Fri, 11 Mar 2016 19:39:08 GMT

Hello Jon,

I've turned on 'proxy-arp' for both interfaces g0/0/0/0 and g0/0/0/1 on the ASR. From the layer 3 switch, now I can ping 73.24.24.245 which I couldn't ping before.

The only issue which I have now is that I still can't ping 8.8.8.8 from my layer3 switch.I did reboot the ISP router and it didn't seem to help either. Not sure what to do next.