Avaya B5800 User Manual download pdf (Page 299)

• Date flow 1: 172.16.16.14:1234 — 10.1.2.3:2345

• Date flow 2: 172.16.16.14:1235 — 10.1.2.3:2345

• Date flow 3: 172.16.16.14:1234 — 10.1.2.4:2345

Data flow 1 has two different port numbers and two different IP addresses and is a valid and

typical socket pair.

Data flow 2 has the same IP addresses and the same port number on the second IP address

as data flow 1, but since the port number on the first socket differs, the data flow is unique.

Therefore, if one IP address octet changes, or one port number changes, the data flow is

unique.

Socket example showing ingress and egress data flows from a PC to a web

server

Notice the client egress stream includes the client’s source IP and socket (1369) and the

destination IP and socket (80). The ingress stream has the source and destination information

reversed because the ingress is coming from the server.

Firewall types

There are three basic firewall types described below.

Packet filtering

Packet Filtering is the most basic form of the firewalls. Each packet that arrives or leaves the

network has its header fields examined against criterion to either drop the packet or let it

through. Routers configured with Access Control Lists (ACL) use packet filtering. An example

of packet filtering is preventing any source device on the Engineering subnet to telnet into any

device in the Accounting subnet.

Application level gateways

Application level gateways (ALG) act as a proxy, preventing a direct connection between the

foreign device and the internal destination device. ALGs filter each individual packet rather

than blindly copying bytes. ALGs can also send alerts via email, alarms or other methods and

keep log files to track significant events.

Hybrid

Hybrid firewalls are dynamic systems, tracking each connection traversing all interfaces of the

firewall and making sure they are valid. In addition to looking at headers, the content of the

Firewall types

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Avaya B5800 User Manual Page 299