Understanding Application-Based Routing
The relentless growth of voice, data, and video traffic and
applications traversing the network requires that networks recognize
traffic types to effectively prioritize, segregate, and route traffic
without compromising performance or availability. SRX Series Services
Gateways support advanced policy-based routing (APBR), also known
as application-based routing, to address these requirements.
APBR is a type of session-based, application-aware routing.
This mechanism combines policy-based routing with an application-aware
traffic management solution. APBR implies classifying flows based
on the attributes of the applications and applying filters based on
these attributes to redirect the traffic. The flow-classifying mechanism
is based on packets representing the application in use.
- Deep packet inspection (DPI) and pattern-matching capabilities
of application identification to identify application traffic or a
user session within an application
- Lookup in the application system cache (ASC) for application
type and the corresponding destination IP address, destination port,
protocol type, and service for a matching rule
If a matching rule is found, the traffic is directed to an appropriate
route and the corresponding interface or device.
APBR provides the following advantages:
- Enables you to define the routing behavior based on application
attributes.
- Extends the scope of static routes by providing more flexible
traffic-handling capabilities by offering granular control for forwarding
packets based on application attributes.
APBR involves the following workflow:
- Creating an APBR profile (also referred to as an application
profile in this document) that will match the type of traffic that
you are going to direct to a different next hop. The profile includes
multiple rules. Each rule can contain multiple applications or application
groups. If the application matches any of the application or application
groups of a rule in a profile, the application profile rule is considered
as a match.
- Associating a routing instance with the application profile
rule. When the traffic on the ingress zone and interface matches an
application profile, the associated static route and next hop defined
in the routing instance are used to route the traffic for the particular
session.
- Associating the application profile to the ingress traffic.
The application profile can be attached to a security zone or it can
be attached to a specific logical or physical interface associated
with the security zone. If the application profile is applied to a
security zone, then all interfaces belonging to that zone are attached
to the application profile by default unless a specific configuration
already exists for that interface.
Figure 54 shows the sequence
in which APBR techniques are applied.
Figure 54: APBR Flow Diagram
The following procedure explains the application-based
routing:
- APBR evaluates the packets based on incoming interface
to determine whether the session is a candidate for application-based
routing. If the traffic has not been flagged for application-based
routing, it undergoes normal processing (non-APBR route).
- If the session needs application-based routing, APBR queries
the application system cache (ASC) module to get the application attributes
details (IP address, destination port, protocol type, and service).
If the application is found, it is further processed for a matching
rule in the APBR profile (see Step 3).
- APBR uses the application details to look for a matching
rule in the APBR profile (application profile). If a matching rule
is found, the traffic is redirected to the specified routing instance
for route lookup.
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