Allow telnet, SSH, or HTTPS remote management on a Cisco 800 series using a Zone Based Firewall

I have recently installed some Cisco 877 routers at some of our branch offices, and wanted to allow remote management of these devices from the LAN at our central location over the VPN. With the Zone based firewall enabled there is no access allowed to the ‘Self’ zone from remote locations by default, as you would expect. This process is pretty straightforward when you are using Cisco PIX or ASA firewalls as you can use the management-access inside command, and then easily define which subnets you want to be able to access which remote management tools. There is no equivalent command when using an IOS router, so you need to configure the appropriate access list, class map, and policy map

In this example the site to site VPN is already configured as is the zone based firewall which was configured by SDM. The following subnets are defined for the LANs at each location:

192.168.1.0/24 – This is the head office LAN subnet which I want to allow access to the remote router over the VPN tunnel

192.168.2.0/24 – This is the branch office LAN subnet which is attached to the Cisco 877

The ip address of the 877 router at the branch office is:

192.168.2.254

Firstly, create an access list to define which services you want to allow access to, from the head office subnet:

router(config)# ip access-list extended remote-manage

router(config-ext-nacl)# permit tcp 192.168.1.0 0.0.0.255 host 192.168.2.254 eq 22

This allows SSH access from the 192.168.1.0/24 subnet to the router

router(config-ext-nacl)# permit tcp 192.168.1.0 0.0.0.255 host 192.168.2.254 eq telnet

This allows telnet access from the 192.168.1.0/24 subnet to the router

router(config-ext-nacl)# permit tcp 192.168.1.0 0.0.0.255 host 192.168.2.254 eq 443

This allows HTTPS access from the 192.168.1.0/24 subnet to the router

Next, create the following class maps:

router(config)# class-map type inspect match-any remote-manage

router(config-cmap)# match access-group name remote-manage

router(config)# class-map type inspect match-any router-access

router(config-cmap)# match class-map remote-manage

Finally, add this policy map

router(config)# policy-map type inspect sdm-permit

router(config-pmap)#class type inspect router-access

router(config-pmap-c)# inspect

You should now be able to telnet, SSH and use SDM to access the router from the head office subnet. If you need to allow any other subnets or hosts to access the router remotely simply add them to the access-list you created earlier. It could be that you want to allow SSH access to the external Internet facing IP of the router which you could do by adding the following (where X.X.X.X is the external IP of the router):

router(config)# ip access-list extended remote-manage

router(config-ext-nacl)# permit tcp any host X.X.X.X eq 22

This would allow any Internet host to access the external IP of the router using SSH, although it would be preferable to lock this down to specific IP addresses or subnets that you already own.

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Downloads stall or stop on a Cisco 877 Router using Zone Based Firewall

I was setting up a Cisco 877 router on an ADSL 2 BT Broadband connection this week and came across an issue when downloading large files from the Internet. With the router configured, and connected everything appeared to be working OK. The ADSL connection was stable, and the VPN tunnel was up and transferring data happily. I performed a few more checks, one of which was to run a speed test using speedtest.net. The test started fine downloading at around 6.5Mb per sec but when it got halfway through it stalled and didn’t complete. Following this I tried to download a 600MB ISO file using my web browser. It downloaded about 100MB and then stalled. Subsequent attempts produced similar results, although sometimes I could only download a couple of MB, and sometimes 50MB to 100MB, but at some point the download would stop and not get any further.

Interestingly, I didn’t seem to get this problem when transferring files over the Site to Site VPN connection, as I transferred around 400MB of data across the VPN without issue. This made me think that it it could be something to do with traffic inspection on the zone based firewall. I did a little digging on the Internet, and found some information relating to out of order packets on Cisco equipment using the Zone Based Firewall. Other reports suggested that if you remove the zone based firewall, downloads proceed normally. It seemed quite a few people have had the same issue that I was having, and there were a few steps that could be taken for verification.

Firstly, in configuration mode set the logging level on the device to ‘debugging’:

 router(config)# logging buffered 51200 debugging 

Next, turn on logging of dropped packets:

 router(config)# ip inspect log drop-pkt

At this stage if you are running in a telnet session you can use the following command to output debug messages to your session:

router(config)# terminal monitor

Alternatively, you can view the log file after testing by running:

router# show logging

After adding the commands to log dopped packets, I kicked off the ISO download again and waited for it to stall. Sure enough after it stopped downloading I got the following message logged (IP addresses have been removed):

%FW-6-DROP_PKT: Dropping tcp session X.X.X.X:80 X.X.X.X:52334 due to Out-Of-Order Segment with ip ident 0

Apparently the zone based firewall has a bit of an issue with out of order packets, but fortunately support for out of order packets has been introduced in IOS versions 15 and above. This 877 router was running IOS version c870-advsecurityk9-mz.124-24.T7.bin. There was only the standard 24MB flash in this router so I upgraded to IOS version c870-advsecurityk9-mz.151-1.T4.bin.

After applying this upgrade the issue was fixed, and downloads proceeded normally.

References:

https://supportforums.cisco.com/thread/2089462

http://www.dslreports.com/forum/r24332834-Config-Zonebased-firewall-and-outororder-dropped-packets