Critical Server Needs and the Linux Kernel
Routers are core elements of modern telecom networks. They propagate and direct billion of data packets from their sources to their destinations using air transport devices or high-speed links. Routers must operate as fast as the medium they use in order to deliver the best quality of service and have a negligible effect on communications. To give some figures, it is common for routers to manage between 10,000 and 500,000 routes. In these situations, good performance is achievable by handling around 2,000 routes/sec.
The actual implementation of the IP stack in Linux works fine for home or small business routers. However, with the high expectation of telecom operators and the new capabilities of telecom hardware, it barely is possible to use Linux as an efficient forwarding and routing element of a high-end router for large networks (core/border/access router) or as a high-end server with routing capabilities.
Two problems with the networking stack in Linux is the lack of support for multiple forwarding information bases (multi-FIB) with overlapping interface IP addresses and the lack of appropriate interfaces for addressing FIB. Another problem with the current implementation is the limited scalability of the routing table.
The solution to these problems is to provide support for multi-FIB with overlapping IP address. As such, we can have different VLANs or different physical interfaces forming independent networks in the same Linux box. A good reason to separate VLANs is for security through separation of services. For instance, a GSN node having multiple company networks connected to it could use VLAN for separation, but that might not hold on the other side of the node. The only way to keep separation (and security) would be to have multiple FIBs.
Consider the example (see Figure 2) of having two HTTP servers serving two different networks with potentially the same IP address. One HTTP server serves the network/FIB 10, while the other HTTP server serves the network/FIB 20. The advantage gained is to have one Linux box serving two different customers using the same IP address. ISPs adopt this approach by providing services for multiple customers sharing the same server (server partitioning), instead of using a server per customer.
The way to achieve this is to have an ID (an identifier that identifies the customer or user of the service) to separate the routing table completely in memory. Two approaches to doing this exist. The first is to have separate routing tables; each routing table is looked up by its ID, and within that table the lookup is done by the prefix. The second approach is to have one table, in which the lookup is done on the combined key = prefix + ID.
A different kind of problem arises when we are not able to predict access time with the chaining in the hash table of the routing cache and FIB. This problem is of particular interest in an environment that requires predictable performance.
Another aspect of the problem is the route cache and the routing table are not kept synchronized most of the time (path MTU, to name one). The route cache flush is executed regularly; therefore, any updates on the cache are lost. For example, if you have a routing cache flush, you have to rebuild every route you currently are talking to by going for every route in the hash/try table and rebuilding the information. First, you have to look it up in the routing cache; if you have a miss, you need to go in the hash/try table. This process is slow and not predictable, because the hash/try table is implemented with linked lists and the potential for collisions is high when a large number of routes are present. This design is suitable for a home PC with a few routes, but it is not scalable for a large server.
To support the various routing requirements of server nodes operating in high-performance, mission-critical environments, Linux should support the following:
An implementation of multi-FIB using tree (radix, patricia and so on). It is important to have predictable performance in insert/delete/lookup from 10,000 to 500,000 routes. In addition, it is favorable to have the same data structure for both IPv4 and IPv6.
Socket and ioctl interfaces for addressing multi-FIB.
Multi-FIB support for neighbors (arp).
Providing these implementations in Linux affects a large part of net/core, net/ipv4 and net/ipv6; these subsystems, mostly the network layer, will need to be re-written. Other areas will feel minimal impact at the source code level; most of the impact will be at the transport layer--socket, TCP, UDP, RAW, NAT, IPIP, IGMP and so on.
As for the availability of an open-source project that can provide these functionalities, an existing project, Linux Virtual Routing and Forwarding, may be able to help. This project aims at implementing a flexible and scalable mechanism for providing multiple routing instances within the Linux kernel. The project has some potential for providing the needed functionalities; however, no progress has been made since 2002, and the project now appears to be inactive.
Practical Task Scheduling Deployment
One of the best things about the UNIX environment (aside from being stable and efficient) is the vast array of software tools available to help you do your job. Traditionally, a UNIX tool does only one thing, but does that one thing very well. For example, grep is very easy to use and can search vast amounts of data quickly. The find tool can find a particular file or files based on all kinds of criteria. It's pretty easy to string these tools together to build even more powerful tools, such as a tool that finds all of the .log files in the /home directory and searches each one for a particular entry. This erector-set mentality allows UNIX system administrators to seem to always have the right tool for the job.
Cron traditionally has been considered another such a tool for job scheduling, but is it enough? This webinar considers that very question. The first part builds on a previous Geek Guide, Beyond Cron, and briefly describes how to know when it might be time to consider upgrading your job scheduling infrastructure. The second part presents an actual planning and implementation framework.
Join Linux Journal's Mike Diehl and Pat Cameron of Help Systems.
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|The Firebird Project's Firebird Relational Database||Jul 29, 2016|
|Stunnel Security for Oracle||Jul 28, 2016|
|SUSE LLC's SUSE Manager||Jul 21, 2016|
|My +1 Sword of Productivity||Jul 20, 2016|
|Non-Linux FOSS: Caffeine!||Jul 19, 2016|
|Murat Yener and Onur Dundar's Expert Android Studio (Wrox)||Jul 18, 2016|
- Stunnel Security for Oracle
- The Firebird Project's Firebird Relational Database
- Murat Yener and Onur Dundar's Expert Android Studio (Wrox)
- SUSE LLC's SUSE Manager
- Managing Linux Using Puppet
- My +1 Sword of Productivity
- Non-Linux FOSS: Caffeine!
- SuperTuxKart 0.9.2 Released
- Google's SwiftShader Released
- Doing for User Space What We Did for Kernel Space
With all the industry talk about the benefits of Linux on Power and all the performance advantages offered by its open architecture, you may be considering a move in that direction. If you are thinking about analytics, big data and cloud computing, you would be right to evaluate Power. The idea of using commodity x86 hardware and replacing it every three years is an outdated cost model. It doesn’t consider the total cost of ownership, and it doesn’t consider the advantage of real processing power, high-availability and multithreading like a demon.
This ebook takes a look at some of the practical applications of the Linux on Power platform and ways you might bring all the performance power of this open architecture to bear for your organization. There are no smoke and mirrors here—just hard, cold, empirical evidence provided by independent sources. I also consider some innovative ways Linux on Power will be used in the future.Get the Guide