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Example: Micro and Macro Segmentation using Group Based Policy in a VXLAN

SUMMARY VXLAN-GBP

Overview

You can achieve micro and macro segmentation, for example to secure data and assets, in a VXLAN architecture using Group Based Policy (GBP). VXLAN-GBP works by leveraging reserved fields in the VXLAN header for use as a Scalable Group Tag (SGT), which you can then use as match conditions in firewall filter rules. Using a SGT is more robust than using port or MAC addresses to achieve similar results. SGTs can be assigned statically (by configuring the switch on a per port or per MAC basis), or they can be configured on the RADIUS server and pushed to the switch via 802.1X when the user is authenticated.

The segmentation enabled by VXLAN-GBP is especially useful in campus VXLAN environments because it gives you a practical way to create network access policies that are independent of the underlying network topology. It simplifies the design and implementation phases of developing network-application and endpoint-device security policies.

You can find more detailed information on the VXLAN-GBP standard in the IEEE RFC, I-D.draft-smith-vxlan-group-policy. For the purposes of this example, suffice to say, VXLAN-GBP leverages reserved fields in the VXLAN header as Scalable Group Tag, as shown in the illustration.

Figure 1: VXLAN Header Fields

Assigning SGTs with a RADIUS Server

In this example we configure SGTs on a RADIUS server, and then use 802.1X access control on the EX4400 to receive them. RADIUS servers are commonly used in campus environments for access control and, for example, to govern the assignment of VLANs.

To accommodate the use of SGTs on the RADIUS server, we need to leverage vendor specific attribute (VSA), as supported by the AAA service framework (these VSA are carried as part of the standard RADIUS request reply message, and provide a built-in extension to handle implementation-specific information such as our SGTs). The exact syntax on the RADIUS server varies according to whether the authentication scheme is MAC or EAP based. For MAC based clients, the configuration looks like this:

For EAP based clients, the SGT is pushed from RADIUS server at the time of authentication. The configuration looks like this:

Starting with Junos Release 21.1R1, EX4400 switches introduce a new match criteria for use with VXLAN-GBP that allows the firewall to recognize the SGT tags that get passed by the RADIUS server and inserted into the VXLAN header.

You can see how this works in the following code samples. GBP firewall policies are framed on the basis of source and destination GBP tags. A source tag is the 16-bit field in the VXLAN header in the incoming packet, while the destination tag is derived at the egress tunnel endpoint, according to the configured tag assignment.

Let's say we have an egress end point with the configuration shown below. Packets from source MAC address 00:01:02:03:04:10:10 are assigned the tag 100, and packets from source MAC address 00:01:02:03:04:20:20 are assigned 200.

For packets with GBP tag 100 and a destination MAC address of 00:01:02:03:04:10:10, the destination group tag (gbp-dst-tag) will be 100, and it will match on term t10-100. Likewise, for packets with GBP tag 100 and a destination MAC address of 00:01:02:03:04:20:20, the destination group tag will be 200, and it will match term t10-200.

The same tag assignment used to map the source MAC address to the source tag is also used to map the destination MAC address to the destination tag. This is true for port based assignments as well.

Let's look at another code sample, this time using a GBP source tag of 300, and with packets ingressing interface ge-0/0/30.0. As you can see below, GBP source tag 300 is assigned and in egress direction, and 300 is also GBP destination group tag.

Note that you need to configure the GBP firewall filter on the egress switch, because there is no way for the ingress switch to know what group tags are used at the egress switch. In addition, you must enable VXLAN-GBP globally on the ingress node, so it can perform the look-up on the matches and add SGT in the VXLAN header, and also on the egress node. Do this with the configuration command shown here:

Before creating any rules, it can be helpful to organize your scheme by creating a table for all your endpoints (users and devices) and the assigned SGT value. Here, we show one such table, the values of which will later be applied in a matrix, that can be used to further simplify the logic and clarify your rules.

Table 1: Endpoints and Their SGT Values

Endpoint

Assigned SGT value

Permanent Employee (PE)

100

Contractor (CON)

200

Security Staff (SS)

300

Security Cam (CAM)

400

Engineering Server (ES)

500

The relationship between the RADIUS server and SGTs, the EX4400 and VXLAN packet headers, and a central firewall filter to manage the access policy, is such that a matrix becomes a handy way to organize the values. In the following table, we list user roles down the first column and device types across the first row to create an access matrix. Each user role and device type is assigned a SGT and the RADIUS configuration has been updated with the information.

This example uses three types of employees, Permanent Employee (PE), Contractor (CON), and Security Staff (SS). It also uses two types of resources, Eng Server (ES) and security camera (CAM). We use Y to indicate access is permitted, and N to shown when access is blocked. The table serves as a useful resource when creating the various firewall rules in the policy and makes access mapping simple and clear.

Table 2: Access Matrix
  ES (SGT 500) CAM (SGT 400) PE (SGT 100) CON (SGT 200) SS (SGT 300)
PE (SGT 100) Y N Y Y N
CON (SGT 200) N N Y N N
SS (SGT 300) N Y N N Y

Topology

For the sake of simplicity, all the configuration in this example is done on a single Juniper EX4400 series switch running Junos OS Release 21.1R1. The switch is connected to a RADIUS server for AAA. This switch functions as egress in this example. Recall that for SGTs you must define the firewall on the egress switch, whereas you would typically do it on the ingress VXLAN gateway for the access layer.

Figure 2: VXLAN GBP on a EX4400 switch VXLAN GBP on a EX4400 switch

Requirements

VXLAN-GBP is supported in Junos OS Release 21.1R1 on the following switches: EX4400-24P, EX4400-24T, EX4400-48F, EX4400-48P, and EX4400-48T.

Configuration

We can summarize the sequence of events underlying VXLAN-GBP based segmentation, laid out in the paragraphs above, as follows:

  • Users log on to the network and are authenticated by the RADIUS server (on which SGTs are configured for all the endpoints).
  • Using firewall filters, the EX4400 selects traffic on the basis of the 802.1X authentication or MAC address, and then assigns a group tag to matching frames. (for dot1x authenticated clients, the static firewall configuration is not needed). The mechanics of this are performed using firewall policy, as shown here: and
  • Tagged traffic passing through the EX4400 is evaluated on the basis SGT values, again, using the mechanics of the firewall filter. For this to happen, you first need to enable chassis forwarding-options vxlan-gbp-profile on the switch, then you use the gbp-dst-tag and/or gbp-src-tag match conditions to write your firewall rules, and include them in the routing policy on the egress switch you use for GBP microsegmentation.

Configuring a Stand-Alone Juniper EX4400 Switch for VXLAN-GBP

Use the following commands to configure VXLAN-GBP segmentation in a sandbox environment. Typically, you would create the firewall filter rules on the switch that serves as the (egress) VXLAN gateway for the access layer, but for the sake of simplicity, we’re using the same stand-alone EX4400 for both the firewall filter rules and the RADIUS server (EAP, here). The values we use in this example are taken from the previous tables.

The commands below include variables such as profile names and IP addresses, which must be adapted to make sense for your test environment.

  1. Configure the radius server:
  2. Configure the physical ports to support RADIUS authentication:
  3. Set up the SGT tags on the RADIUS server:
  4. Enable VXLAN-GBP on the switch:
  5. Create Firewall filter rules that leverage the SGTs (using values organized in the matrix):
  6. Run a commit check in Junos to verify that the commands and the variables you used are valid. When satisfied with your configuration commit the candidate configuration to make it active on the device. These commands are shown below. You can also review your configuration by typing run show configuration.