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Application Identification

Identifying Applications by Name

The Session Smart Routing platform has several techniques by which it can associate inbound traffic to named applications. This is sometimes referred to as "Application Identification" (or "appID"), and the feature that allows administrators to define network policies using Fully Qualified Domain Names (FQDNs) instead of IP addresses.

The SSR has three built-in techniques for affiliating named applications to services, all of which will be described in this document. (A fourth technique, involving service function chaining third party software is not covered here.) The three techniques are:

  1. Using DNS to resolve FQDNs to IP addresses
  2. Using the application-identification mode tls
  3. Using the application-identification mode module

DNS-based Services

Generally, when configuring a service on a SSR, administrators use the address field to identify the IP address(es)/CIDR block(s) that the SSR should use to match to inbound traffic. However, the address field will also accept hostnames, such as www.128technology.com. When a service uses a hostname in the address field, it is referred to as a DNS-based service.

For every DNS-based service, the SSR will use its local DNS to resolve the hostnames; for every IP address that is returned the SSR will treat that as though it were configured in the address field, and install FIB entries accordingly. It will also refresh these FIB entries based on the time-to-live (TTL) returned by the DNS server. Here is a sample configuration for reference:

admin@labsystem1.fiedler# show config running authority service interchange

config

authority

service interchange
name interchange

scope private
security internal
address community.128technology.com

access-policy trusted
source trusted
permission allow
exit
share-service-routes false
exit
exit
exit

In this configuration, the address is configured as community.128technology.com. This will be resolved once the configuration is committed, and the SSR will resolve that hostname and install FIB entries. The SSR will periodically re-resolve those hostnames to ensure that the FIB entries are kept up-to-date.

note

The names used in the address field must be DNS-resolvable names. You cannot use wildcards such as *.128technology.com.

Advantages:

  1. This is a very easy and intuitive way to associate traffic to services, without having to define a long list of IP addresses. When upstream devices change their IP address, there's no need to reconfigure the SSR to keep it up-to-date, as this is handled by DNS.
  2. Unlike AppID based on TLS, there is no "chicken and egg issue;" i.e., no prerequisite to have the destination be reachable in order to learn the destination's name.

Disadvantages:

This technique relies on your SSR getting the same answers from DNS that your clients get. Take for example a massive SaaS provider such as www.salesforce.com. Their web site resolves to hundreds or thousands of IP addresses distributed across the globe. When the SSR resolves that hostname, it will get a handful of answers; if a client does the same DNS query and gets a different set of answers, then the traffic the client sends will not match the FIB entries that the SSR has created.

Key to success

Use DNS-based services when your destination uses a small set of nonvolatile IP addresses. This technique is perfect for small, hosted services. The effectiveness of using DNS-based services diminishes rapidly when referencing names that resolve to dozens of address or more.

AppID based on TLS

The SSR can also learn about named destinations by inspecting the traffic that traverses it. This is done by inspecting the X.509 certificate sent by a server during the TLS handshake process. Importantly: this presupposes that the SSR can route packets to that destination for the purposes of retrieving the server's certificate. Thus, when using AppID based on TLS, it is important to ensure that there is a service and service-route capable of reaching that server in addition to the one you'll configure for the named application.

note

Normally this is done by having a "catch-all" service for 0.0.0.0/0 to route traffic out to the internet, but it does not need to be.

Within the Server Hello message sent by a server will include its X.509 certificate, which is decipherable by the client to include information about the server. One such example is here:

[ptimmons@labsystem1 ~]$ openssl x509 -in /tmp/512b-rsa-example-cert.pem -text -noout
Certificate:
Data:
Version: 1 (0x0)
Serial Number: 3578 (0xdfa)
Signature Algorithm: sha1WithRSAEncryption
Issuer: C=JP, ST=Tokyo, L=Chuo-ku, O=Frank4DD, OU=WebCert Support, CN=Frank4DD Web CA/emailAddress=support@frank4dd.com
Validity
Not Before: Aug 22 05:26:54 2012 GMT
Not After : Aug 21 05:26:54 2017 GMT
Subject: C=JP, ST=Tokyo, O=Frank4DD, CN=www.example.com
Subject Public Key Info:
Public Key Algorithm: rsaEncryption
Public-Key: (512 bit)
Modulus:
00:9b:fc:66:90:79:84:42:bb:ab:13:fd:2b:7b:f8:
de:15:12:e5:f1:93:e3:06:8a:7b:b8:b1:e1:9e:26:
bb:95:01:bf:e7:30:ed:64:85:02:dd:15:69:a8:34:
b0:06:ec:3f:35:3c:1e:1b:2b:8f:fa:8f:00:1b:df:
07:c6:ac:53:07
Exponent: 65537 (0x10001)
Signature Algorithm: sha1WithRSAEncryption
14:b6:4c:bb:81:79:33:e6:71:a4:da:51:6f:cb:08:1d:8d:60:
ec:bc:18:c7:73:47:59:b1:f2:20:48:bb:61:fa:fc:4d:ad:89:
8d:d1:21:eb:d5:d8:e5:ba:d6:a6:36:fd:74:50:83:b6:0f:c7:
1d:df:7d:e5:2e:81:7f:45:e0:9f:e2:3e:79:ee:d7:30:31:c7:
20:72:d9:58:2e:2a:fe:12:5a:34:45:a1:19:08:7c:89:47:5f:
4a:95:be:23:21:4a:53:72:da:2a:05:2f:2e:c9:70:f6:5b:fa:
fd:df:b4:31:b2:c1:4a:9c:06:25:43:a1:e6:b4:1e:7f:86:9b:
16:40
note

This sample certificate was supplied by FM4DD.

About a third of the way through the output you can see that the Common Name (listed as CN in the Subject line) is www.example.com. This is what SSR will parse and subsequently retain as the "application name" for this destination. Assuming this matches a configured application-name within a service, a FIB entry is installed with this server's IP address and associated with the service.

To enable application identification based on TLS, configure the application-identification element within the router context as seen here:

admin@labsystem1.fiedler# show config running authority router burlington application-identification

config

authority

router burlington
name burlington

application-identification
mode tls
exit
exit
exit
exit

For reference, here's a service that would leverage the X.509 certificate shown above:

admin@labsystem1.fiedler# show config running authority service example

config

authority

service example
name example
description "www.example.com website"
application-name www.example.com

access-policy trusted
source trusted
permission allow
exit
service-policy NO-LTE
share-service-routes false
exit
exit
exit

Here we can see the application-name set to www.example.com, which matches the Common Name from the X.509 certificate in our example. Assuming we had a service/service-route capable of reaching www.example.com to begin with, the TLS handshake would see the server's X.509 certificate returned back to the client through the SSR. The SSR parses the certificate, recognizes www.example.com as belonging to the service named example and installs a FIB entry for it with the server's IP address.

note

The example service needs to have its own service-route in order for traffic to be forwarded.

With the TLS-based application identification technique, the application-name can include a wildcard such as *.example.com, which is not possible with the DNS-based approach. This gives administrators a bit more flexibility in defining which traffic to match to services when parsing the X.509 certificates.

AppID using Modules

The last, and arguably most powerful built-in technique for performing application identification is to use a module – effectively, a script that is resident on the SSR's host operating system that will generate a JSON file that contains dynamic, ingestible routes. This is extremely flexible, but requires some programming expertise.

note

It is also possible to simply place a static JSON document on the SSR's filesystem (i.e., one that is not generated by a local script) as a means of feeding an application identification module into the SSR).

Configuring application identification based on modules first requires that a router have the feature enabled:

admin@labsystem1.fiedler# show config running authority router becket application-identification

config

authority

router becket
name becket

application-identification
mode module
exit
exit
exit
exit

Script-Based Module Setup

Scripts are placed on the router's filesystem at /etc/128technology/application-modules/. These scripts produce a JSON output stored at /var/run/128technology/application-modules/, which in turn is processed by the SSR and installed as FIB entries.

Systemd-Based Module Setup

Beginning with the 5.2 release, systemd may be used to manage the execution of application identification modules. JSON output produced by the module is passed directly to the highway REST API instead of being written to disk.

Using this approach, modules are registered by creating a file at /etc/128technology/application-modules/services/<module-name>. This file lists the systemd units of the module and specifies if and how SSR should interact with them.

  • reload-service: When the highway process starts, reload the systemd unit. This is a signal to POST the JSON to highway again as module data is not saved through process restarts.
  • stop-on-shutdown: Stop the systemd unit when SSR is shutting down.

Modules must be registered in order for SSR to accept the POST of JSON module data.

In the following example, a systemd timer unit is used to periodically invoke the main service/script, which does the work of gathering module data. Both are stopped on shutdown, but only the timer unit needs to fire again on restart of SSR.

[
{
"service-name": "office365.timer",
"reload-service": true,
"stop-on-shutdown": true
},
{
"service-name": "office365.service",
"reload-service": false,
"stop-on-shutdown": true
}
]

For more information about using timers with the systemd service, refer to ArchLinux systemd/Timers.

Viewing Modules

Beginning with the 5.2 release, module registration and detailed module status (including a full list of ip-prefix/ports/protocol) can be accessed via a REST API or from the CLI. Please refer to the API documentation available from the GUI, and the show application modules status and show application modules registration for full details.

Referencing Modules in Configuration

Each module produces a list of service names that are used to reference it in the configuration through the application-name list. For example, an application identification module named zoom will retrieve and process all of the IP addresses used for the ZOOM videoconferencing service. The corresponding service looks like this:

admin@labsystem1.fiedler# show config running authority service ZOOM

config

authority

service ZOOM
name ZOOM

description "Zoom meetings"
scope private
application-name ZOOM

access-policy trusted
source trusted
permission allow
exit
share-service-routes false
exit
exit
exit

The application-name is configured as it is with the tls variant of application-identification. In this case, however, it will read the contents of a JSON file to produce the FIB entries. Below is an excerpt from the zoom module's output:

{
"duration": 86400,
"services": {
"ZOOM": [
{
"ip-prefix": "3.7.35.0/25"
},
{
"ip-prefix": "3.21.137.128/25"
},
{
"ip-prefix": "3.22.11.0/24"
},
...
]
},
"module-name": "zoom"
}
note

In the case of this module, the script that generates the JSON is /etc/128technology/application-modules/zoom.py, the output is stored as /var/run/128technology/application-modules/zoom.json. A copy of the zoom.py script is available on our user community, AI-Driven SD-WAN powered by Session Smart community.

The services tag of ZOOM is what associates these IP prefixes to the service we've shown above. Each of these IP prefixes (which could have also included port ranges, but don't in this example) will create a FIB entry for the ZOOM service, and be given access and policy determinations based on the configuration we've set in our SSR.

The SSR ships with an Office365 module, and other modules can be found on AI-Driven SD-WAN powered by Session Smart community, our user community, as well as on Github. For more information on writing your own application identification module, refer to our developer documentation or our sample code.