Don’t ignore the middleboxes
Traditional networks contain routers, switches, clients and servers. Most introductory networking textbooks focus on these devices and the protocols that they use. However, real networks can be much more complex than the typical academic networks that are considered in textbooks. During the last decade, enterprise networks have included more and more middleboxes. A middlebox can be roughly defined as a device that resides inside the network and it able to both forward (like a router or a switch) but also modify packets. For this reason, middleboxes are often considered as layer-7 relays but they are not officially part of the Internet architecture. These middleboxes are usually deployed by network operators to better control or improve the performance of traffic in their network. There exist various types of middleboxes RFC 3234. The most common ones are :
- Network Address Translators (NAT) that rewrite IP addresses and port numbers
- Firewalls that control the incoming and outgoing packets
- Network Intrusion Detection System that analyse the packet payloads to detect possible attacks
- Load balancers that allow to distribute the load among several servers
- WAN optimizers that compress packets before transmitting them over expensive low bandwidth links
- Media gateways that are able to transcode voice and video formats
- transparent proxy caches that speedup access to remote web servers by maintaining caches
- …
The list of middleboxes keeps growing and managing them in addition to the routers and the switches is becoming a concern for enterprise network operators. In a recent paper presented at USENIX NSDI12, Vyas Sekar and colleagues describe a survey that they performed in an anonymous entreprise network. This network contained about 900 routers and more than 600 middleboxes !
| Appliance type | Number |
|---|---|
| Firewall | 166 |
| Network Intrusion Detection System | 127 |
| Conferencing/Media gateway | 110 |
| Load balancers | 67 |
| Proxy caches | 66 |
| VPN devices | 45 |
| WAN optimizers | 44 |
| Voice gateways | 11 |
| Routers | about 900 |
Internet Topology Zoo
A recent article published on slate provided nice artistic views about the layout of the optical fibers that are used for Internet.
Researchers have spent a lot of time to collect data about ISP networks during the slate decade. If you are looking for nice maps about real networks, I encourage you to have a look at the Internet topology zoo. This website, maintained by researchers from the University of Adelaide contains maps of a few hundred networks, an excellent starting point if you would like to understand a bit more on ISP networks are designed.
If you are more interested by the layout of cables, notably submarine cables, you can also check the geographical maps provided by telegeography.
Controlling Queueing delays
Routers use a buffer to store the packets that have arrived but have not yet been retransmitted on their output linke. These buffers play an important role in combination with TCP’s congestion control scheme TCP uses packet losses to detect congestion. To manage their buffers, routers rely on a buffer acceptance algorithm. The simplest buffer acceptance algorithm is to discard packets as soon as the buffer is full. This algorithm can be easily implemented, but simulations and measurements have shown that is does not always provide good performance with TCP.
In the 1990s, various buffer acceptance algorithms have been proposed to overcome this problem. Random Early Detection (RED) probabilistically drops packets when the average buffer occupancy becomes too high. RED has been implemented on routers and has been strongly recommended by the IETF in RFC 2309. However, as of this writing, RED is still not widely deployed. One of the reasons is that RED uses many parameters and is difficult to configure and tune correctly (see the references listed on http://www.icir.org/floyd/red.html).
In a recent paper published in ACM Queue, Kathleen Nichols and Van Jacobson propose a new Adaptive Queue Management algorithm. The new algorithm measures the waiting time of each packet in the buffer and its control law depends on the minimum buffer occupancy. An implementation for Linux-based routers seems to be in progress. Maybe it’s time to revisit buffer acceptance algorithms again…
Unicode is growing
The Internet was created by using the 7-bits ASCII character set. Over the years, the internationalisation of the Internet forced protocol designers to reconsider the utilisation of the 7-bits US-ASCII character set. A first move was the utilisation of the 8-bits character sets. Unicode became the unifying standard that allows to encode all written languages. A recent article in IEEE Spectrum provides interesting data about the progressing of Unicode on web servers. See http://spectrum.ieee.org/telecom/standards/will-unicode-soon-be-the-universal-code