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Cisco Firepower deployment modes are the methods to insert a Firepower into the network as a Firewall/IPS device or as a IPS-only device. In Firewall/IPS mode, you have the option to choose routed or transparent mode and as a IPS-only device you can choose between inline and passive mode.

We discussed routing mode and transparent mode in the previous sections. In this section, we will discuss IPS-only inline and passive modes.

Cisco Firepower Firewall and IPS Deployment Modes

routed/transparent mode as firewall and inline/passive mode as IPS-only device

What we have implemented so far is firepower firewall routing mode and transport mode, in which not only firewall services are available but you can also implement IPS services as we saw in the previous section.

Firepower Firewall and IPS Deployment Modes
Firepower Firewall and IPS Deployment Modes

Just to review, in routed mode, the firewall does routing. So we need to give IP addresses to firewall interfaces and do static or dynamic routing like any other router.

In transparent mode, firepower acts like a switch. It’s easier to add a switch or transparent firewall in an existing network because it doesn’t change any IP addressing or routing infrastructure.

But sometimes you use a separate firewall and you want to use firepower as an IPS-only service. In this condition we have three main options to use. Inline mode, inline tap mode or passive mode.

Cisco Firepower Deployment Mode: IPS-only Inline Mode

In inline mode, Firepower is physically inserted into the path, so all traffic is forwarded through the Firepower IPS device. For example, we can insert the firepower physically between the data center and the enterprise core, or between the enterprise core and the WAN edge.

Firepower IPS-only Inline Mode
Firepower IPS-only Inline Mode

Firepower Inline mode versus Transparent mode

In inline mode, there can be added only two interfaces in each inline pair. What is received in each interface, will be forwarded to other interface after inspection, without MAC switching or IP routing. It behaves like a wire with an inspection module in between.

Firepower Transparent Mode versus Inline Mode
Firepower Transparent Mode versus Inline Mode

Inline mode can be used when we are using a Firepower as an IPS-only device in which most firewall services are not working.

Inline mode differs from transparent mode, in which multiple interfaces can be added in each bridge group and each bridge group behaves like an isolated switch.

Transparent mode is used as a mode when we use Firepower as a firewall service, which can also be used as an IPS device at the same time.

Cisco Firepower Deployment Mode: IPS-only Inline Tap Mode

Firepower in Inline tap mode will be deployed exactly as inline mode. the difference is that in inline tap mode, traffic itself will not be inspected but just a copy of traffic is inspected. Therefore in inline tap mode, it is not possible to drop intrusions and they will be just alerted.

Firepower Inline mode versus Inline Tap mode
Firepower Inline mode versus Inline Tap mode

Cisco Firepower Deployment Mode: IPS-only Passive Mode

In passive mode, firepower will not be inserted physically in path.

Firepower IPS-only Passive Mode
Firepower IPS-only Passive Mode

Actually sometimes, it is not possible to insert an IPS device physically in the path to inspect all traffic. For example in the LAN, it is not possible to insert an IPS so it can inspect all LAN traffic.

In passive mode, copy of traffic will be sent to the IPS with the help of SPAN/RSPAN/ERSPAN technology.

Therefore, in passive mode like inline tap mode, only copy of traffic are inspected, so it is not possible to drop a traffic if it is intrusion, and only an alert is given.

Although there are some methods to block intruders in inline tap mode and passive mode, they are not real-time. For example, they can block intruders’ source IP by inserting an access rule in a firewall.

Passive mode is also used when we want just to monitor what is coming in our network with inserting an IPS in passive mode in edge of the network.

Firepower IPS inline mode and inline tap mode configuration

Firepower Firewall and IPS Topology Review

So far we have used Firepower as Firewall, in which G0/0 was connected to outside interface and G0/1 was connected to inside network.

From now own we will use firepower as IPS-only device with G0/2 connected to outside interface and G0/3 connected to inside interface.

Firepower as Firewall and IPS Topology Overview
Firepower as Firewall and IPS Topology Overview

Cisco Firepower IPS Inline mode configuration

First we configure and enable G0/2 and G0/3 interfaces as outside1 and inside1 interface.

In interface configuration, there is an option to change interface mode to passive mode in which is ready to receive the copy of traffic and inspect the receiving traffic. The copy of traffic can be sent to this interface with any methods like SPAN/RSPAN switch feature.

Prepare interfaces for IPS-only inline configuration
Prepare interfaces for IPS-only inline configuration

Then we configure an inline pair and add these two interfaces into the inline pair.

Configure IPS-only Inline Pair

in Advanced Tab, we have some options to configure:

  • Tap mode: with enabling this option, the copy of traffic will be inspected. I will implement it in the next section
  • Propagate Link State: automatically brings down the second interface in the inline interface pair when one of the interfaces goes down.
  • Strict TCP Enforcement: it is a security feature and blocks connections where three-way handshake are not completed
  • Snort Fail Open: when it is selected, traffic will be pass without inspection when the Snort process is busy or down.
Configure Inline Pair Advanced Options
Configure Inline Pair Advanced Options

Then IPS policy must be configured and be applied to the access control rule.

We will use the IPS policy that we have configured in previous section, IPS Policy1.

Configure IPS Policy
Configure IPS Policy

In this policy we have configured to Block “ICMP ECHO REPLY” traffic which is implemented in previous section.

Configure ICMP ECHO REPLY Packets to be blocked

In the previous section we have also activated IPS policy in a rule in which permit all traffic. It is obvious that it does not mean to inspect the traffic in a rule in which drop the traffic.

Enable IPS Policy in Access COntrol Rule
Enable IPS Policy in Access COntrol Rule

Firepower IPS Inline mode monitoring and troubleshooting

To test that our IPS policy works, it is enough just to ping an external IP from a computer behind Firepower. We expect that ping reply will not be received.

Ping Reply is Blocked in Firepower IPS-only Inline Mode
Ping Reply is Blocked in Firepower IPS-only Inline Mode

Then we have to check intrusion events to make sure that the ping reply is dropped with our IPS policy.

We can check intrusion events in “Analysis -> Intrusion -> Event”. 

Intrusion Events Analysis in Cisco Firepower IPS-only Inline mode
Intrusion Events Analysis in Cisco Firepower IPS-only Inline mode

Firepower IPS Inline tap mode configuration and monitoring

To implement IPS inline tap mode, the implementation is exactly the same. The only difference is that we have to enable tap mode in inline pair.

Configure Cisco Furepower IPS-only Inline Tap mode
Configure Cisco Furepower IPS-only Inline Tap mode

In inline tap mode, as we know, no traffic can be dropped. In other words, all traffic with Block action, will be just alerted.

To make sure, we will ping the same address as inline mode.

now we expect that our ping traffic will be replied.

Ping Reply is alerted in Firepower IPS-only Inline Tap mode
Ping Reply is alerted in Firepower IPS-only Inline Tap mode

But there must also be an intrusion event where the traffic should be dropped but cannot be dropped because the copy of the traffic is inspected and the original traffic is already forwarded.

Intrusion Events Analysis in Cisco Firepower IPS-only Inline Tap mode
Intrusion Events Analysis in Cisco Firepower IPS-only Inline Tap mode
Lesson tags: Cisco Firepower Deployment Modes, cisco firepower ips inline, firepower inline mode, firepower inline pair, firepower inline set, firepower inline tap, firepower inline vs passive, firepower interface configuration, Firepower IPS deployment modes
Back to: Cisco FTD Design and Implementation > Cisco Firepower IPS Policy

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