While configuring a TrendMicro IMSVA appliance I tried to configure different URL filtering policies using built-in Windows Active Directory groups, like “Domain Users” in conjunction with user/group name authentication. Configuring policies with built-in groups weren’t functioning properly. The policies just weren’t matched, while I knew for sure that the user is a member of the specified group. So I started a research. After reading the documentation (IWSVA Adminstrator’s Guide) more carefully I found the solution to my problem. The Administrator’s Guide contains the following notes:
Since the ‘member’ attribute is incomplete in some built-in groups that exist in Active Directory (such as ‘Domain Users’), IWSVA will not be able to obtain membership information for these groups through LDAP search. Trend Micro recommends you create policies based on user-defined groups instead of built-in groups.
To configure IWSVA to listen on port 3268, the Microsoft Active Directory server that IWSVA uses should have the Global Catalog enabled.
Since the member attribute is not replicated to the Global Catalog for all group types, and because the memberOf attribute derives its value by referencing the member attributed (called back links and forward links, respectively), search results for members of groups, and groups which a member belongs, can very. Search results depend on whether you search the Global Catalog (port 3268) or the domain (port 389), the kind of groups that the user belongs to (global groups or domain local groups), and whether the users belongs to universal groups outside the local domain.
I tried to verify this information with Softerra’s LDAP browser and found the “flaw”. All users within the Active Directory are member of the Domain Users group and most of them have the Domain Users group as Primary Group. When looking at the CN=Domain Users with the LDAP browser I only see 12 members, while the Active Directory contains 700+ user accounts.
I changed the policy to match a user-defined group, which I checked with the LDAP browser first, and the matching works perfectly. I guess this is another RTFM story!
I noticed some strange behavior in a vpdn-group configuration on a Cisco 876 router. I have a router with the following vpdn-group configuration:
! Default PPTP VPDN group
description pptp vpn users
The configuration is working perfectly and users can dialin using a PPTP connection. Backups of the configuration are made by Kiwi CatTools. Lately I noticed that the following command l2tp tunnel receive-window 256 is added to the configuration, like displayed below:
Cisco has the following explanation for the command:
“Use the l2tp tunnel receive-window command to set the size of the advertised control channel receive window. The receive window size controls the number of L2TP control packets that can be queued by the system for processing. Increasing the size of the control channel receive window allows the system to open PPP sessions more quickly; a smaller size is desirable on networks that cannot handle large bursts of traffic… Source”
Two days later the command is gone again. I asked the network engineers if they made any changes to the configuration, but they didn’t. I looked at the configuration and tried to add the command, but I am not able to add the command.
cisco-876(config-vpdn)#l2tp tunnel receive-windows 256
% Invalid input detected at ‘^’ marker.
I searched a little further and the command can only be added, when the dial-in protocol is changed from pptp to l2tp. Looking at the configuration above, you can see clearly that the dial-in protocol pptp is configured and the l2tp command is added.
I cannot explain this behavior. I hope some of you can…….
Last week a friend called me and told me he was having serious problems with his network. A complete blade environment wasn’t able to communicate with the rest of the network. I asked what changed in the network and he told me that he had added a VLAN to a trunk allowed lists.
Because he is a friend, I dialed in and checked the configuration of the switch. I noticed that all ports on the switch were err-disabled. What happened here, that all switch ports were err-disabled!!! I noticed the configuration of link state tracking on all ports.
Link-state tracking, also known as trunk failover, is a feature that binds the link state of multiple interfaces. Link-state tracking provides redundancy in the network when used with server network interface card (NIC) adapter teaming. When the server network adapters are configured in a primary or secondary relationship known as teaming and the link is lost on the primary interface, connectivity transparently changes to the secondary interface.
At first I was skeptic about the link state configuration and asked my friend why it was used. He couldn’t give me any answer, because he didn’t configure the switch. For me it was hard to find a reason why link state tracking was used, because I wasn’t familiar with the network. I removed the link state configuration from the switch. All ports changed to a normal state. I noticed that the uplink (port-channel) configuration wasn’t correct. They added the VLAN to the trunk allowed lists on a member port and not on the port-channel interface.
After helping my friend and dreaming for a couple of days, I started thinking about the Link State Tracking feature. I tried to discover why someone configured the feature in my friends environment. Eventually, after some brain cracking, I found the solution. Let’s look at the following example environment.
The figure shows one ESX server, which has two NIC’s. One NIC is connected to bl-sw01 and the other NIC is connected to bl-sw02. The ESX uses the load-balancing algorithm “Route based on Virtual PortID”.
Now lets assume the link between bl-sw02 and dis-sw02 loses its connection. Because the ESX server still has a connection with bl-sw02, it keeps sending packet that way. Switch bl-sw02 doesn’t have any uplink to the rest of the network, so the packet will get dropped.
When using Link State Tracking the connection between the ESX server and switch bl-sw02 will also loose its connection when the uplink between bl-sw02 en switch dis-sw02 gets lost. The ESX server will only use the connection with switch bl-sw01 to reach the rest of the network. Link State Tracking uses upstream and downstream interfaces. In the example the connection between the switch port, which connects switch bl-sw02 to switch dis-sw02, would be configured as an upstream port. The switch port to the ESX server would be configured as a downstream port. The downstream port is put in err-disable state when the upstream port loses its connection. This is exactly what you would like to accomplish.
The first step to enable Link State Tracking globally on the switch:
bl-sw02(config)# link state track 1
The next step is configuring the upstream and downstream interfaces.
switchport trunk encapsulation dot1q
switchport mode trunk
link state group 1 upstream
spanning-tree link-type point-to-point
switchport trunk encapsulation dot1q
switchport mode trunk
link state group 1 downstream
spanning-tree portfast trunk
You can check the status of the Link State Group with the following command:
bl-sw02#show link state group detail
Link State Group: 1 Status: Enabled, Up
Upstream Interfaces : Gi0/16(Up)
Downstream Interfaces : Gi0/10(Up)
In the future I will use Link State Tracking, especially in blade environments. At least in blade environments with multiple switch, which don’t support some kind of stacking technology, and servers with multiple NIC’s.
When configuring a Remote Access VPN or a Site to Site VPN connection you have the ability to filter traffic entering and leaving the VPN connection. You have the ability to enable inbound IPsec sessions to bypass interface access lists. Group policy and per-user authorization access lists still apply to the traffic.
The sysopt connection permit-ipsec command allows all the traffic that enters the security appliance through a VPN tunnel to bypass interface access lists. Group policy and per-user authorization access lists still apply to the traffic. In PIX 7.1 and later, the sysopt connection permit-ipsec command is changed to sysopt connection permit-vpn.
Mostly I use this option and configure some extra ACL’s to filter trafifc. Some customers don’t want to use this option and want to specify all traffic with ACL’s. This is more secure, but is a bigger burden on the management of the firewall.
From IOS 7.1 and later you have the ability to configure VPN filtering through Group Policies. In short you configure an extended ACL, link this ACL to a Group Policy and link the Group Policy to the specific Tunnel Group. The syntax (source and destination) needs to be correct for the ACL to work.
For Site to Site VPN’s the remote network is the source and the local network is the destination. For Remote Access VPN’s the VPN IP pool is the source and the local network the destination, as specified below.
An ACL that is used for a vpn-filter must not also be used for an interface access-group. When a vpn-filter is applied to a group-policy/user name mode that governs Remote Access VPN Client connections, the ACL must be configured with the client assigned IP addresses in the src_ip position of the ACL and the local network in the dest_ip position of the ACL. When a vpn-filter is applied to a group-policy that governs an L2L VPN connection, the ACL must be configured with the remote network in the src_ip position of the ACL and the local network in the dest_ip position of the ACL.
Exercise caution when you construct the ACLs for use with the vpn-filter feature. The ACLs are constructed with the post-decrypted traffic (inbound VPN traffic) in mind. However, they are also applied to the traffic originated in the opposite direction.
More about this matter and examples configurations can be found here.