allow PPTP client through Cisco ASA 8.4 to external PPTP server

In order to allow a PPTP VPN client through a Cisco ASA firewall in order to access an external PPTP server you need to add the following to your configuration.

policy-map global_policy

class inspection_default

inspect pptp

Upgrade VDSL modem firmware on a Cisco 880 Series Router

Firstly transfer the new firmware to your router’s flash memory using tftp. Next enter config mode and type:

router(config)# controller vdsl 0

Then type the following command at the prompt, where YOUR_FIRMWARE is the name of the firmware file that you transferred to flash e.g. vdsl.bin-A2pv6C035d_d23j which is the recommended firmware for BT ADSL in the UK.

router(config-controller)# firmware filename flash:YOUR_FIRMWARE


Cisco BT xDSL Product Bulletin

A2pv6C035d_d23j Firmware Release Notes


Restart a VPN tunnel on a Cisco ASA or PIX

To reset and restart VPN tunnels on a Cisco ASA or PIX firewall simply type:

clear crypto isakmp sa

Allow access to DMZ or other remote Vlan over VPN tunnel on Cisco ASA 8.4

I recently needed to provide internal access to a DMZ Vlan at one of my remote sites over a VPN tunnel. The VPN tunnel was provided by 2 Cisco ASA 5505 firewalls both running ASA software versions more recent than 8.4. The LAN subnets in this example can be defined as follows:

Main Office Subnet:

Remote Office Subnet:

Remote Office DMZ Subnet:

This article assumes that you already have the site to site VPN tunnel set up between the main office ( subnet and the remote office ( subnet, and that you have already created a network object for your main office subnet called main-office-lan, and for your remote office subnet called remote-office-lan on both ASAs. It also assumes that your DMZ interface on the remote ASA is called ‘dmz‘, and that you have an ACL defining interesting VPN traffic called main-remote-vpn on both ASAs.

Firstly create a network object for the remote office DMZ on both the main office and remote office ASAs. In configuration mode add the following two commands

object network remote-office-dmz


Next create a network object group for the 2 subnets at your remote site on both the main office and remote office ASAs

object-group network remote-office-networks
network-object object remote-office-lan
network-object object remote-office-dmz

Next, on the remote office ASA exempt traffic from the remote office DMZ subnet, to main office subnet from Network Address Translation (NAT) on the outside interface. i.e. traffic that will be travelling from the to the subnet over the VPN tunnel. In configuration mode add the following command:

nat (dmz,outside) source static remote-office-dmz remote-office-dmz destination static main-office-lan main-office-lan

Then on the remote office ASA change the ACL that defines interesting traffic for your site to site vpn tunnel (in this case called main-remote-vpn) to include the the dmz subnet, by using the network object group that you created earlier:

access-list main-remote-vpn extended permit ip object-group remote-office-networks object main-office-lan

Next you need to modify the configuration of the main office ASA to exempt traffic travelling over the VPN tunnel to the remote office DMZ from NAT, and also add the remote office subnet to the ACL that defines interesting traffic for your site to site VPN tunnel:

Modify the NAT rule on the main office ASA in config mode:

nat (inside,outside) source static main-office-lan main-office-lan destination static remote-office-networks remote-office-networks

Then modify the ACL that defines your site to site VPN traffic in config mode:

access-list main-remote-vpn extended permit ip object main-office-lan object-group remote-office-networks

Thats it, you should now be able to connect to hosts in the DMZ at you remote site over your site to site VPN connection. If you have multiple site to site VPNs from your main office network you may need to tweak this config , but the theory is the same.

PLEASE NOTE: This configuration will allow hosts in the DMZ at your remote site to connect to any hosts in your main office network! Clearly in most cases this will not be desirable, unless the additional remote Vlan is not a DMZ and performs some other function, which is not exposed directly to the Internet (which was the situation in my case). In any event you may wish to use VPN filters  to restrict traffic from the remote DMZ Vlan to your main office, or by disabling sysopt connection permit-vpn using the no sysopt connection permit-vpn command and applying ACLs to your outside interface. Excercise caution when applying either of these types of filtering to make sure you don’t restrict yourself from the site to site VPN tunnel.

Upgrade flash memory in a Cisco 877 Router

Undo the 2 screws on the back on the router as shown:

Opening the case of a Cisco 877 Router


Then undo the 3 screws securing the protective metal case beneath:

Accessing the flash and RAM slots in a Cisco 877 router


Swap the flash memory for the new larger bit:

Swapping the flash memory


Replace the case, plug in the power, connect the router to your computer using a console cable, and then power it on.

Fire up hyperterm or some similar program and connect to the router. It may complain about an inconsistent sector list in flashfs on boot up, and will also tell you that there is no bootable IOS image file in the flash memory. Once you are at the ROMMON prompt issue the following command:

format flash:

click ‘y’ and press enter to confirm the format operation

Once the format is complete, connect a LAN patch lead from you computer to the router. Assign an IP address to the LAN adapter of your computer such as Fire up a bit of TFTP server software on your computer, such as Cisco TFTP server, or Solarwinds TFTP server

At the rommon prompt type the following,  making sure you assign an IP address to the router that is in the same subnet as the IP that you assigned your computer, e.g.


then assign a subnet mask:


then a default gateway:


then a TFTP server (i.e. the IP address you assigned your computer’s LAN adapter):


and finally the filename of the IOS image that you want to transfer back on to your router


If you want to review the variables that you have set above any time just type:


Next issue the tftpdnld command to copy the IOS image to the flash memory of your router using tftp:


Click ‘y’ to continue. This will take a few minutes. After that reboot the router and you’re done:





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

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 host eq 22

This allows SSH access from the subnet to the router

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

This allows telnet access from the subnet to the router

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

This allows HTTPS access from the 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.

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 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.