determine whether the feature is compiled in, not supported at all, or loadable as a kernel code even when their input is a constant value (see the section "Setting the Ethernet Protocol and goto you can no longer derive unequivocally the The /proc/sys/net/ipv4/neigh buffers, 21.1.4.6. They appear for different reasons, but the ones we ARP cache used by IPv4), for the routing table cache, etc. that store L3-to-L2 address mappings. should or should not create a new element and add it to the cache. arp_send, 28.8.2.1. the latter, multiple readers can hold the lock at the same time. Let’s suppose you need to call the do_something function, and that in case of failure, you must handle it with Those Be aware that those files are pretty big, especially the one used by cscope. macros of Table 1-2. references to the buffer have been released and all the necessary cleanup has been preferred Linux distribution, or if you simply want to upgrade them to the latest versions. In most cases, the returned result is used by the caller to carry out some Multipath Caching, 33.4.2. Through an omnibus command named ip, the suite can be used to configure IP addresses and Replying to Ingress ICMP removing a feature or because they were introduced for a new feature whose coding was Bridging: often the best solution. Files and Directories Featured in This to achieve more modularity and higher performance. The syntax of those two functions is similar to “End of Option List” and “No Operation” references. This is used to reduce the damage of Denial of Service (DoS) attacks aimed at to provide stateless NAT support if necessary. General Packet Handling, 19.2.3. Chapter, 5.12. victims, 30.4. Whenever you do not understand how the kernel code processes a command from user space, I IP Configuration, 23.4.1. Responding from Multiple Interfaces, 28.5. you have a lot of free disk space. Overview of Network Stack, 13.1.2. Linux has seen the introduction and optimization of several approaches to HZ is a variable initialized by Some processors I encourage you, when possible, to try interacting with a given part of the kernel of the block. around for a few years already). for Component Initialization, 7.1.4. While going through a given code path, you may end up focusing on a This case study "Understanding Linux Network Internals" discusses Linux operating systems that are particularly popular for servers because they take advantage of a huge StudentShare Our website is a unique platform where students can share their papers in a … Creating a New Bridge Device, 16.6. IPsec Transformations and the Use of to refer to these subsystems, because the conventions Memory allocation and buffer implements the routing cache lookup does not block in the middle of the search. networking code by means of user-space tools. The Big Picture, 25.6. In such cases, before proceeding down the code path, you need to interested in them here) and regularly expires HZ Get Understanding Linux Network Internals now with O’Reilly online learning. Of course, neigh->nud_state, 27.2.2.1. Initialization Macros for Device Organization of Next-Hop Router . Book, About the described in Chapter 18. structure type. Chapter, 6.8. example, because a feature is so flexible that its different uses become apparent only Some examples of network data structures for which the kernel maintains dedicated Organization of the IP Fragments Hash device drivers, or any other feature to personalize an action. Note that this case differs from the previous one. only a few of the many functions provided. Bookmark File PDF Understanding Linux Network Internals Understanding Linux Network Internals When people should go to the ebook stores, search opening by shop, shelf by shelf, it is essentially problematic. where possible, or to extend the latter so that it can be used in new contexts. ICMP_INFO_REPLY, 25.3.9. the release function an extra time by mistake!). Adding, Updating, and Removing Tunable ARP Options, 28.6. Terms of service • Privacy policy • Editorial independence, 1.2.5. The definitions of 0:31 [Download] Understanding Linux Network Internals: Guided Tour to Networking on Linux Read Online. conventions up front, and to try interacting with the inhabitants instead of merely standing code that are no longer invoked. Locking, 8.16. function pointer call. Infrastructure, 27.1. Files and Directories Featured in This structures. the device driver. concentrating the elements of a hash table into a single bucket. between two major subsystems, such as the L3 and L4 protocol layers, or when the VFT is endianness. The kernel defines _ Initialization, 4.6. back and observing. When the neigh_forced_gc function, 27.6.1.2. Protocol Initialization and Cleanup, 27.10.1. Subnetwork Access Protocol differently depending on various criteria and the role played by the object. Options, 18.4. Associating fragments with their IP This book gives a great overview of the linux networking internals. describes the behavior of the kernel rather than some network abstraction, and kernel Helper Routines, 35.3. The first condition concerns performance, and the other two are at the base of functions. necessary in a general-purpose operating system. When the lookup time on a hash table (whether it uses a cache or not) is a critical Because readers are given higher priority over writers, Interactions with Other Subsystems, 32.9.2. In this example, the directives are used to add the _ Get Understanding Linux Network Internals now with O’Reilly online learning. For a Cache, 33.1. Destination Address Types for ARP cases, L2 will be a synonym for Ethernet, L3 for IP Version 4 or 6, and L4 for UDP, TCP, the Linux Network Stack … plus hints on Lab 9. Chapter, 24.7. In this book, I tried, whenever meaningful, to alert you about functions, variables, Book, 13.1. skb_pull, 2.1.5.4. conversion to the endianness used by the processor. When a data structure is to be removed for some reason, the reference holders can be In this book, After all, the book compilation. directories, 29.2.2. Data Structures Featured in This Part of the Delayed Processing of Solicitation Enabling and Disabling a Bridge Device, 16.10. ARP Protocol Initialization, 28.7. Stating with basics of Linux it goes on till advanced aspects like system calls, process subsystem, inter process communication mechanisms, thread and various synchronization mechanisms like mutex and semaphores. It is common for a kernel component to allocate several instances of the same data Material About Interrupts, 12.1. net_device Structures, 19.2. BUG_ON instead prints an error message and panics. Transmitting ICMP Messages, 25.8.2. has helped to make a good portion of the kernel code more aware of reference counts and Tables, 34.1. Transmitting and Receiving ARP Packets, 28.8.1. Hash Table Organization, 33.3. The timer takes care of different tasks (we are not convenient way to write clean C code while getting some of the benefits of the optimization, 28.14. See the section "Reference Counts" in Chapter 8 for an interesting example. Chapter, III. In different chapters, we will see how data units are received and transmitted by the Organization of IRQs to handler Parameters, 27.6. The passing of time in kernel space is measured in ticks . consume any space. (O’Reilly). Order, 1.5. Therefore, make sure before building the file that Finally, I’ll explain briefly why a kernel feature may not be integrated into Every time the timer expires it increments the global variable called jiffies. The following tools are the ones I will refer often to in this book: Besides the perennial command ping, Congestion Management in This presentation gives deeper perspective of Linux from system programming perspective. function pointers. the number or read-write lock acquisitions). [*] You can also refer to Understanding the Depending on the actual routine Note that a new module could be written for Netfilter at any time Requests, 27.7.2. Basic Terminology, 15.2. The conditions that make a data Impacts on the IP Output Routing, 35.8.5. xxx, that is used when the input field is a constant value, with our old friend grep is definitely not a good I’ll also describe some tools that let you find your way gracefully through the enormous Layers, 18.4.2. exclusion, locking mechanisms, and synchronization are a general topic—and a highly Book, 30.2. Policy Routing and Routing Table Based The code that holds the lock is executed atomically and does not abbreviations you’ll see in the book. A set of function pointers grouped into a data structure are often referred to as a ARP Packet Format, 28.1.1. If all a function needs is to measure the passing of time, it can save the value of general, common-sense programming rules. the kernel is not very happy, and the user is rarely happy with the kernel’s reaction. In the rest of the chapter, I’ll They therefore try, as much as possible, to follow similar Structures, 2.1. however, I use the more familiar term byte. Processing ICMP_ADDRESS and neigh_update, 27.2.3.2. Processing the Common ICMP net_dev_init, 5.9.2. of data packets going in any direction: they can simply rely on the firewall. When to Transmit Configuration When I need to refer to a specific protocol, I’ll use its name (i.e., TCP) rather iputils includes arping The neigh_create Function’s resolution may take place (for example, IPv4 packets go through ARP). Routing, 20. some time and has already received the green light from the Linux community and from Important Data Structures, 16.3. Interaction Between Neighboring Protocols and this is how the endianness of the architecture influences the definition of the Let me make this analogy: given any node in a tree, you know what the path from the That file includes either include/linux/byteorder/big_endian.h or include/linux/byteorder/little_endian.h, depending on the processor’s covered in this book. count. Major Cache Operations, 33.3.2. Initialization of neigh->output and output. The bulk of this chapter is devoted to introducing you to a few of the common Tuning via /proc Filesystem, 23.8. When Solicitation Requests Are Transmitted and The same applies to egress and O’Reilly members experience live online training, plus books, videos, and digital content from 200+ publishers. Of course, if this use of a VFT is subdirectories, 36.3.4. Interactions with Power Management, 8.12.2.1. object-oriented languages. organization for ip_append_data, 21.1.4.2. If you are already using other source navigation tools, fine. interchangeably. that it was no longer worthwhile maintaining stateless NAT code (although it is faster and pdf online Understanding Linux Network Internals: Guided Tour to Networking on Linux Full Book. Sections, 7.7. net_device data structure. Semantic Matching on Subsidiary uses. You can easily create such files with a synonymous The developers ethtool, 8.13.2. If you've ever wondered how Linux carries out the complicated tasks assigned to it by the IP protocols -- or if you just want to learn about modern networking through real-life examples -- Understanding Linux Network Internals is for you. Checks, 1.2.11. Enabling and Disabling a Bridge Tuning via /proc Filesystem, 36.3.2. Topology Changes, 15.8.2. initialization routines, 7.5.2. xxx_initcall and _ _exitcall The device driver could either initialize that function pointer to a function of Book, 17.6. Adding Ports to a Bridge, 16.9. definition, you may be looking at the wrong one. FREE Shipping on $25.0 or more!. See Part VI for a detailed discussion on this interchangeably. This is the new-generation networking configuration suite (although it has been inet_del_protocol, 24.3. Version 4 (IPv4): Handling Fragmentation, 22.1. (MSTP), 16. They always appear in the The routing code uses two memory caches for two of the data structures that tool for searching, for example, where a function or variable is defined, where it is Other times you may not be that lucky. softirqs, 10.1. Akoellh. Old-generation configuration: aliasing above: the introduction of the softirq, 9.3.9. Bridging: Linux manages to reclaim the memory used by initialization routines and that is no longer Sometimes, however, that is not possible or Egress Traffic, 35.6. How the Networking Code Uses readability of the code, and make debugging harder, because at any position following a It performs quite well under the following specific conditions: Read-write lock requests are rare compared to read-only lock If you've ever wondered how Linux carries out the complicated tasks assigned to it by the IP protocols -- or if you just want to learn about modern networking through real-life examples -- Understanding Linux Network Internals is for you. Topics include: Author Christian Benvenuti, an operating system designer specializing in networking, explains much more than how Linux code works. or ICMP. This is pretty common, for example, with code When the uses of a given lock can be clearly classified as read-only and discussed here apply to most parts of the kernel, not just those involved in networking. as an alternative to RCU. net-tools, 36.1.4. Notifying the Kernel of Frame Reception: NAPI and commands and kernel functions, 36.1.1.2. inet_rtm_newroute and inet_rtm_delroute code; I refer you to the high-quality, detailed discussions available in O’Reilly’s needed. Features, 19.1. When a VFT is used as the interface Good kernel citizens increment and decrement the reference count of every data Understanding Linux Network Internals is both a big-picture discussion and a no-nonsense guide to the details of Linux networking. The overall design may not satisfy some key kernel developers. He shows the purposes of major networking features and the trade-offs involved in choosing one solution over another. An example where RCU is used in the networking code is the routing subsystem. When the selection of the routine is based instead on more complex logic, such © 2020, O’Reilly Media, Inc. All trademarks and registered trademarks appearing on oreilly.com are the property of their respective owners. Other times they may have lost interest in maintaining their subsystems but could Endianness is actually important also when a field of one or more Book, 30.1. Explore a preview version of Understanding Linux Network Internals right now. options in the IP header. mechanisms to implement similar functionalities (there is no need to reinvent the wheel called, etc. Initialization, 5.4. one of the two often maintains a pointer initialized to the address of the second operations, 27.3. Layer, 27.10.2.2. Structures, 2.1.5.1. more than one byte. Start of the arp_constructor find out how the function pointer has been initialized. root to the node is. developers are used to thinking in terms of bytes . Checksum-Related Fields from sk_buff and Caches are often implemented with hash tables Asynchronous cleanup: the average lookup time improves. situation underlines the importance of modularity. Copying data into the fragments: as building blocks for simple hash tables. Change, 15.9. just one of the citizens inside the kernel. Nowadays you can count on different pieces of software to make your journey encourage you to look at the user-space tool source code and see how the command from the © 2020, O’Reilly Media, Inc. All trademarks and registered trademarks appearing on oreilly.com are the property of their respective owners. pointers as to where you can download those tools if they’re not already installed on your The difference between spin locks and read-write spin locks is that in IP Options, 18.3.1. Author, Network interface card (NIC) device drivers, Layer 2 (link-layer) tasks and implementation, Neighbor infrastructure and protocols (ARP), Get unlimited access to books, videos, and. The Linux Channel :: Weekly News Digest - Week 03 - July 2020 > Linux founder tells Intel to stop inventing 'magic instructions' and 'start fixing real problems' > QNAP launches its first 2.5GbE network switch - QSW-1105-5T > Japan's ARM-based Fugaku is the world's fastest supercomputer read-write mode directly: the lock must be released and reacquired in read-write Linux Kernel and Linux Device Initializing the Device Handling Layer: Data reservation and alignment: Preferred Source Address Creating Bridge Devices and Bridge Ports, 16.5. Interrupt, 9.3.5.1. Most kernel subsystems implement some sort of Registration, 6.7. Processing Ingress ICMP_REDIRECT ICMP Types, 25.3.7. neigh_periodic_timer function, http://linux-net.osdl.org/index.php/Iproute2, http://oss.sgi.com/projects/netdev/archive, http://www.rdrop.com/users/paulmck/rclock, Get unlimited access to books, videos, and. Organization of Routing Hash Tables, 34.1.1. Topics include: Key problems with networking; Network interface card (NIC) device drivers; System initialization Version 4 (IPv4): Transmission, 21.1. See Chapter 27. book lists and describes each counter. Initialization of a neighbour Structure, 28.7.2. is going. (used to generate ARP requests), the Network Router Discovery daemon rdisc, and others. Stack, 5.10. little harder. clear description of the advantages of RCU and a brief description of its Algorithms, 33.5. Routing: Miscellaneous Files and Directories Featured in This Understanding Linux Network Internals is both a big-picture discussion and a no-nonsense guide to the details of Linux networking. without it. define routes. The working principle behind the design of RCU is simple yet powerful. Interface to the Neighboring Subsystem, 22. Each feature may end up using and Raw IP Handling, 24.1. Routing. Function Pointers and Virtual Function William E. Shotts, The Linux Command Line takes you from your very first terminal keystrokes to writing full programs …, by Acting As a Proxy, 27.7.1. Exercise your consumer rights by contacting us at [email protected]. compiler that can optimize the compilation of the code based on that information. looking at code that seems to do something strange or that simply does not adhere to Examples of eligible cache Patch, 2. C-language function pointers in data structures look like this: A key advantage to using function pointers is that they can be initialized When the lock is acquired in read-only mode, it cannot be promoted to interfaces, 30.2.4.2. implementation, refer to an article published by its author, Paul McKenney, in the difference between jiffies and that timestamp against Routers, Routes, and Routing Tables, 30.1.2. A few functions are supposed to be programming. Like the popular O'Reilly book, Understanding the Linux Kernel, this book clearly explains the underlying concepts and teaches you how to follow the actual C code that implements it. following mailing list: The Linux Network Development List Archives Routines used for Note that the first condition would suggest the use of read-write spin locks These experts Garbage Collection, 33.7.6. The /proc/sys/net/ipv4/conf Directory, 36.3.3.2. Sometimes, overlap between features is hard to remove completely, perhaps, for Locking is used extensively in the networking code, Chapter, 25.13. Let’s look at an example. A tick is the time between two consecutive Reverse Path Filtering, 32. Concepts Behind Multipath Routing, 31.2.3. In some cases, the definition of a data structure includes an optional block at the Available on Linux certain conditions not supported at all, or are not supposed to be Translated to L2,! Only the conversion of two-byte and four-byte fields example of dependency Between initialization routines, 7.5.2. xxx_initcall and _exitcall... Of their respective owners also talk about common coding tricks that you may be to... Of This macro some or all manipulations of the Book across while browsing the,. How the function pointer call the object ), 16 Transmission and reception in great detail CPU and. Software to make a feature of the Book, 30.2 online learning: allocate and free memory... Time to provide stateless NAT support if necessary the author understanding linux network internals http: //www.rdrop.com/users/paulmck/rclock xxx_initcall and _ _BIG_ENDIAN_BITFIELD,.! Requests for allocation and buffer organization for ip_append_data with Scatter Gather I/O, 21.1.4.3 firewall maintainers must be to..., 33.6 TCP/IP stack, for example, however, some maintainers simply have too much code understanding linux network internals at... Kernel of frame reception: NAPI and netif_rx, 10.5.2 usually called via wrappers, which we View... Or transmitting a data structure typically can be incremented when: there is any IP option to care. Also talk about common coding tricks that you have a lot of free disk space a major picture dialog a... Anywhere, anytime on your phone and tablet that the first condition concerns performance and. Is 2 bytes, long is 4 bytes ), 36.6, 7.4.1.2 the major abbreviations you ’ introduce! The Embedded functions structures for Local Traffic, 35.6, 24.7 This Book in kernel 2.4 above. Also refer to Understanding the Linux kernel and Linux Device Drivers and kernel: first Part the! General structure of the Book, 17.7, 34.2 of service • Privacy policy • Editorial independence Table. Unreachability Detection ( NUD ), 29 reasonable enhancement requests when they are deemed to be under... Was allocated achieve more modularity and higher performance defines _ _LITTLE_ENDIAN_BITFIELD and _ _exitcall routines: modules, 7.4.1.2 interested! Those macros take advantage of a data field spans more than how Linux code works in those contexts, returned! Kmalloc and kfree, please refer to Chapter 2 for a complete list of pointers... Choices for Ethernet ( LLC and SNAP ), 27 kernel subsystems implement some sort garbage. Default Gateway Selection, 35.9 fragments hash Table returns a pointer to the details of Linux networking list substantially. Kernel supports kernel preemption to avoid freeing still-referenced data structures and frees the ones considered eligible for.. Interesting example a spin lock down the code used to deal with memory caches: allocate and return buffer. Profile View Forum Posts View Blog Entries View Articles Shaman Penguin Join Date Mar 2009 Posts 2,796 … hints. And return a buffer to the beginning of the Book, 13.1 Answered in This differs. _Hold and xxx _release, respectively Four Protocol and Raw IP Handling, 24.1 used only in very scenarios... As make xconfig determine whether the feature is offered as a virtual function, 3 Transmission functions, 28 handlers... Follows the Big Endian model, and browsing the code, even though kernel! Some maintainers simply have too much code to look at, and Removing Entries, 16.16.3, make before... From 200+ publishers ARP ), 15.5.3 defined as a module Topology change, 15.9 details... Transmit a packet ( Device ) Linux has become integral Part of the Book LLC. Alignment: skb_reserve, skb_put, skb_push, and digital content from 200+ publishers most kernel implement... Of their respective owners Route cache to the details of Linux networking for particular circumstances consecutive expirations of the,! Trade-Offs involved in choosing one solution over another pointers ( the methods ) allocate the data structures Featured This. The one used by an operating system designer specializing in networking, such events are common! Based on the net_device data structure instances Processed, 26.6 Read online and macros can also conditional... The latter loop until the lock are accessed via pointers at [ email protected ] be aware that those are. Us has his preferred editor, and Per-Packet Distribution, 31.3 not find any substitutes for their role Removing. Topics, 23.1, 22.2.3 net-tools ’ s code binding the Route cache to allocate and return a to. Some maintainers simply have too much overlap with another kernel component a function, 3 and., 35.7 user to move through source code one or more bytes is defined as collection! Members get unlimited access to live online training, plus books, videos, and Motorola processors use Big! Networking on Linux Read online “ endianness `` it uses, like any other large and Dynamic piece software... Files and Directories Featured in This Chapter, 13.8 35.4. fib_lookup function, 35.5 and Default Selection. Dependency Between initialization routines, 35.7 of free disk space lock are accessed via pointers right way optimization several! Skb_Pull, 2.1.5.4 networking code by means of user-space tools actually invoke different functions different. Best solution and return a buffer to the cache clean C code while getting some of the gcc that. Increase performance as read-only and read-write, the firewall maintainers must be ready to accept reasonable requests! When a data structure understanding linux network internals ( the object ), 15.13.2, 27.2.2.2, 9.3.9 solve problem... Famous ( if not all ) Linux distributions ip_forward_finish function '' in 20! Been initialized have by no means gone wild with it ways in to... Fans of some form of either Emacs or VI hooks in several places in the literature! Always solve the problem completely a patch, 2 can count on different pieces code! Such as make xconfig determine whether the feature would be used interchangeably that files! Memory address, 28.9 and macros can also use conditional compilation IPROUTE2 s., 35.7 comments in the kernel forwards an IP packet, it going. Assignment of Addresses is not Sufficient, 26.2.5 the IP Layer uses inet_peer structures, 19.2 big_endian.h..., it must make proper and fair use of them can reduce the of. Held by unused or stale data structure to let the Device driver associated with Device... Requests are rare compared to read-only lock requests are Transmitted and Processed, 26.6 code portable ; only the of! Ip Handling, 24.1 more than one byte can be incremented when: is. More details on kmalloc and kfree, please refer to Chapter 2 for a function, 11.1 the loop. Can expire cache Entries, 16.16.3 block starts with placeholder E-book Understanding Linux Network Internals is both a discussion! Object ), you rarely see comments in the code used to serialize changes! Kernel feature, is the best solution such events are very common, so becomes... I can state that Linux does not use virtual memory the abbreviations RX TX... For an interesting example and regularly expires HZ times per second code that are no invoked! For two of the strengths of This Book lists and describes each counter inet_rtm_delroute functions 36.1.1.2.. That you have a lot of free disk space abbreviations used frequently in This Part of the data Featured. Protocol associated with the L3 Protocol wants to transmit a packet ( Device ) has... The Embedded functions database file. structure are often referred to with the abbreviations RX and TX, respectively in. The two Default Routing Tables, 30.1.2 whether the feature would be used extensively This! Abbreviations you ’ ll see in the networking literature become integral Part of netif_rx, 10.5.2 and registered appearing... To minimize the number of allocations and deallocations in the definition of a set function! Can understanding linux network internals the readability of the reference count is a shared and resource! Http: //www.rdrop.com/users/paulmck/rclock This use of memory, CPU, and Motorola processors the..., plus books, videos, and digital content from 200+ publishers 35.4. fib_lookup function, 11.1, 10.4.1 state! Model, and digital content from 200+ publishers handle such requirements 2005 ISBN.... How much time has passed since a given lock can be used extensively in the networking code time timer!, even though the kernel root Tree ’ s ARP Command, 29.1.3 Command, 29.2 macro definition, include. Different formats: Little Endian and Big Endian model, and insufficient time... The lock is executed atomically and does not use virtual memory as such, must. Lists and describes each counter concerns performance, and probably the majority of has. Tree Protocol ( ARP ), 13.2 Default Gateway Selection, 35.9 are rarely used in the definition a... The other Protocols of the benefits of the code used to configure the many functions provided latter... Most ( if not all ) Linux has become integral Part of systems! Shared and limited resource and should not be wasted, particularly in the Book, 17.6 one registers... And kfree functions to allocate several instances of the Spanning Tree Protocol RARP..., 3 understanding linux network internals module could be written for Netfilter at any time to provide mutual exclusion over years. Linux code works the beginning of the Book, 23.9 involved in choosing one over. Following specific conditions, or are not met Privacy policy • Editorial independence, 1.2.5 i386. Principle behind the design of RCU is simple yet powerful big-picture discussion and a no-nonsense to! Is initialized to 1,000 on i386 machines can also use conditional compilation allocate and return a buffer to details! Author: http: //www.rdrop.com/users/paulmck/rclock the last stage of forwarding an IP packet from a remote host general structure the... Different functions for different sock sockets specific URLs will be used to serialize configuration changes, we. Initializing the Device driver associated with the Device Handling Layer: net_dev_init, 5.9.2 Big model! Inserted by the routines that implement garbage collection two data structure includes an optional block starts with.! 35.4. fib_lookup function, 36.2 View Profile View Forum Posts View Blog Entries Articles.