This is code for addressing several networked computers at once, enlarging your kernel by about 2 KB. You need multicasting if you intend to participate in the MBONE, a high bandwidth network on top of the Internet which carries audio and video broadcasts. More information about the MBONE is on the WWW at <http://www.savetz.com/mbone/>. Information about the multicast capabilities of the various network cards is contained in <file:Documentation/networking/multicast.txt>. For most people, it's safe to say N.
If you intend to run your Linux box mostly as a router, i.e. as a computer that forwards and redistributes network packets, say Y; you will then be presented with several options that allow more precise control about the routing process. The answer to this question won't directly affect the kernel: answering N will just cause the configurator to skip all the questions about advanced routing. Note that your box can only act as a router if you enable IP forwarding in your kernel; you can do that by saying Y to "/proc file system support" and "Sysctl support" below and executing the line echo "1" > /proc/sys/net/ipv4/ip_forward at boot time after the /proc file system has been mounted. If you turn on IP forwarding, you should consider the rp_filter, which automatically rejects incoming packets if the routing table entry for their source address doesn't match the network interface they're arriving on. This has security advantages because it prevents the so-called IP spoofing, however it can pose problems if you use asymmetric routing (packets from you to a host take a different path than packets from that host to you) or if you operate a non-routing host which has several IP addresses on different interfaces. To turn rp_filter on use: echo 1 > /proc/sys/net/ipv4/conf/<device>/rp_filter or echo 1 > /proc/sys/net/ipv4/conf/all/rp_filter Note that some distributions enable it in startup scripts. For details about rp_filter strict and loose mode read <file:Documentation/networking/ip-sysctl.txt>. If unsure, say N here.
Keep track of statistics on structure of FIB TRIE table. Useful for testing and measuring TRIE performance.
Normally, a router decides what to do with a received packet based solely on the packet's final destination address. If you say Y here, the Linux router will also be able to take the packet's source address into account. Furthermore, the TOS (Type-Of-Service) field of the packet can be used for routing decisions as well. If you are interested in this, please see the preliminary documentation at <http://www.compendium.com.ar/policy-routing.txt> and <ftp://post.tepkom.ru/pub/vol2/Linux/docs/advanced-routing.tex>. You will need supporting software from <ftp://ftp.tux.org/pub/net/ip-routing/>. If unsure, say N.
Normally, the routing tables specify a single action to be taken in a deterministic manner for a given packet. If you say Y here however, it becomes possible to attach several actions to a packet pattern, in effect specifying several alternative paths to travel for those packets. The router considers all these paths to be of equal "cost" and chooses one of them in a non-deterministic fashion if a matching packet arrives.
If you say Y here, which is recommended, then the kernel will print
verbose messages regarding the routing, for example warnings about
received packets which look strange and could be evidence of an
attack or a misconfigured system somewhere. The information is
handled by the klogd daemon which is responsible for kernel messages
("man klogd").
This enables automatic configuration of IP addresses of devices and of the routing table during kernel boot, based on either information supplied on the kernel command line or by BOOTP or RARP protocols. You need to say Y only for diskless machines requiring network access to boot (in which case you want to say Y to "Root file system on NFS" as well), because all other machines configure the network in their startup scripts.
If you want your Linux box to mount its whole root file system (the one containing the directory /) from some other computer over the net via NFS and you want the IP address of your computer to be discovered automatically at boot time using the DHCP protocol (a special protocol designed for doing this job), say Y here. In case the boot ROM of your network card was designed for booting Linux and does DHCP itself, providing all necessary information on the kernel command line, you can say N here. If unsure, say Y. Note that if you want to use DHCP, a DHCP server must be operating on your network. Read <file:Documentation/filesystems/nfs/nfsroot.txt> for details.
If you want your Linux box to mount its whole root file system (the one containing the directory /) from some other computer over the net via NFS and you want the IP address of your computer to be discovered automatically at boot time using the BOOTP protocol (a special protocol designed for doing this job), say Y here. In case the boot ROM of your network card was designed for booting Linux and does BOOTP itself, providing all necessary information on the kernel command line, you can say N here. If unsure, say Y. Note that if you want to use BOOTP, a BOOTP server must be operating on your network. Read <file:Documentation/filesystems/nfs/nfsroot.txt> for details.
If you want your Linux box to mount its whole root file system (the one containing the directory /) from some other computer over the net via NFS and you want the IP address of your computer to be discovered automatically at boot time using the RARP protocol (an older protocol which is being obsoleted by BOOTP and DHCP), say Y here. Note that if you want to use RARP, a RARP server must be operating on your network. Read <file:Documentation/filesystems/nfs/nfsroot.txt> for details.
Tunneling means encapsulating data of one protocol type within another protocol and sending it over a channel that understands the encapsulating protocol. This particular tunneling driver implements encapsulation of IP within IP, which sounds kind of pointless, but can be useful if you want to make your (or some other) machine appear on a different network than it physically is, or to use mobile-IP facilities (allowing laptops to seamlessly move between networks without changing their IP addresses). Saying Y to this option will produce two modules ( = code which can be inserted in and removed from the running kernel whenever you want). Most people won't need this and can say N.
This is helper module to demultiplex GRE packets on GRE version field criteria. Required by ip_gre and pptp modules.
Tunneling means encapsulating data of one protocol type within
another protocol and sending it over a channel that understands the
encapsulating protocol. This particular tunneling driver implements
GRE (Generic Routing Encapsulation) and at this time allows
encapsulating of IPv4 or IPv6 over existing IPv4 infrastructure.
This driver is useful if the other endpoint is a Cisco router: Cisco
likes GRE much better than the other Linux tunneling driver ("IP
tunneling" above). In addition, GRE allows multicast redistribution
through the tunnel.
One application of GRE/IP is to construct a broadcast WAN (Wide Area Network), which looks like a normal Ethernet LAN (Local Area Network), but can be distributed all over the Internet. If you want to do that, say Y here and to "IP multicast routing" below.
This is used if you want your machine to act as a router for IP packets that have several destination addresses. It is needed on the MBONE, a high bandwidth network on top of the Internet which carries audio and video broadcasts. In order to do that, you would most likely run the program mrouted. Information about the multicast capabilities of the various network cards is contained in <file:Documentation/networking/multicast.txt>. If you haven't heard about it, you don't need it.
Normally, a multicast router runs a userspace daemon and decides what to do with a multicast packet based on the source and destination addresses. If you say Y here, the multicast router will also be able to take interfaces and packet marks into account and run multiple instances of userspace daemons simultaneously, each one handling a single table. If unsure, say N.
Kernel side support for Sparse Mode PIM (Protocol Independent Multicast) version 1. This multicast routing protocol is used widely because Cisco supports it. You need special software to use it (pimd-v1). Please see <http://netweb.usc.edu/pim/> for more information about PIM. Say Y if you want to use PIM-SM v1. Note that you can say N here if you just want to use Dense Mode PIM.
Kernel side support for Sparse Mode PIM version 2. In order to use this, you need an experimental routing daemon supporting it (pimd or gated-5). This routing protocol is not used widely, so say N unless you want to play with it.
The kernel maintains an internal cache which maps IP addresses to hardware addresses on the local network, so that Ethernet/Token Ring/ etc. frames are sent to the proper address on the physical networking layer. Normally, kernel uses the ARP protocol to resolve these mappings. Saying Y here adds support to have an user space daemon to do this resolution instead. This is useful for implementing an alternate address resolution protocol (e.g. NHRP on mGRE tunnels) and also for testing purposes. If unsure, say N.
Normal TCP/IP networking is open to an attack known as "SYN flooding". This denial-of-service attack prevents legitimate remote users from being able to connect to your computer during an ongoing attack and requires very little work from the attacker, who can operate from anywhere on the Internet. SYN cookies provide protection against this type of attack. If you say Y here, the TCP/IP stack will use a cryptographic challenge protocol known as "SYN cookies" to enable legitimate users to continue to connect, even when your machine is under attack. There is no need for the legitimate users to change their TCP/IP software; SYN cookies work transparently to them. For technical information about SYN cookies, check out <http://cr.yp.to/syncookies.html>. If you are SYN flooded, the source address reported by the kernel is likely to have been forged by the attacker; it is only reported as an aid in tracing the packets to their actual source and should not be taken as absolute truth. SYN cookies may prevent correct error reporting on clients when the server is really overloaded. If this happens frequently better turn them off. If you say Y here, you can disable SYN cookies at run time by saying Y to "/proc file system support" and "Sysctl support" below and executing the command echo 0 > /proc/sys/net/ipv4/tcp_syncookies after the /proc file system has been mounted. If unsure, say N.
Support for IPsec AH. If unsure, say Y.
Support for IPsec ESP. If unsure, say Y.
Support for IP Payload Compression Protocol (IPComp) (RFC3173), typically needed for IPsec. If unsure, say Y.
Support for IPsec transport mode. If unsure, say Y.
Support for IPsec tunnel mode. If unsure, say Y.
Support for IPsec BEET mode. If unsure, say Y.
Support for Large Receive Offload (ipv4/tcp). If unsure, say Y.
Support for INET (TCP, DCCP, etc) socket monitoring interface used by native Linux tools such as ss. ss is included in iproute2, currently downloadable at: http://www.linuxfoundation.org/collaborate/workgroups/networking/iproute2 If unsure, say Y.
Support for selection of various TCP congestion control modules. Nearly all users can safely say no here, and a safe default selection will be made (CUBIC with new Reno as a fallback). If unsure, say N.
BIC-TCP is a sender-side only change that ensures a linear RTT fairness under large windows while offering both scalability and bounded TCP-friendliness. The protocol combines two schemes called additive increase and binary search increase. When the congestion window is large, additive increase with a large increment ensures linear RTT fairness as well as good scalability. Under small congestion windows, binary search increase provides TCP friendliness. See http://www.csc.ncsu.edu/faculty/rhee/export/bitcp/
This is version 2.0 of BIC-TCP which uses a cubic growth function among other techniques. See http://www.csc.ncsu.edu/faculty/rhee/export/bitcp/cubic-paper.pdf
TCP Westwood+ is a sender-side only modification of the TCP Reno protocol stack that optimizes the performance of TCP congestion control. It is based on end-to-end bandwidth estimation to set congestion window and slow start threshold after a congestion episode. Using this estimation, TCP Westwood+ adaptively sets a slow start threshold and a congestion window which takes into account the bandwidth used at the time congestion is experienced. TCP Westwood+ significantly increases fairness wrt TCP Reno in wired networks and throughput over wireless links.
H-TCP is a send-side only modifications of the TCP Reno protocol stack that optimizes the performance of TCP congestion control for high speed network links. It uses a modeswitch to change the alpha and beta parameters of TCP Reno based on network conditions and in a way so as to be fair with other Reno and H-TCP flows.
Sally Floyd's High Speed TCP (RFC 3649) congestion control. A modification to TCP's congestion control mechanism for use with large congestion windows. A table indicates how much to increase the congestion window by when an ACK is received. For more detail see http://www.icir.org/floyd/hstcp.html
TCP-Hybla is a sender-side only change that eliminates penalization of long-RTT, large-bandwidth connections, like when satellite legs are involved, especially when sharing a common bottleneck with normal terrestrial connections.
TCP Vegas is a sender-side only change to TCP that anticipates the onset of congestion by estimating the bandwidth. TCP Vegas adjusts the sending rate by modifying the congestion window. TCP Vegas should provide less packet loss, but it is not as aggressive as TCP Reno.
Scalable TCP is a sender-side only change to TCP which uses a MIMD congestion control algorithm which has some nice scaling properties, though is known to have fairness issues. See http://www.deneholme.net/tom/scalable/
TCP Low Priority (TCP-LP), a distributed algorithm whose goal is to utilize only the excess network bandwidth as compared to the ``fair share`` of bandwidth as targeted by TCP. See http://www-ece.rice.edu/networks/TCP-LP/
TCP Veno is a sender-side only enhancement of TCP to obtain better throughput over wireless networks. TCP Veno makes use of state distinguishing to circumvent the difficult judgment of the packet loss type. TCP Veno cuts down less congestion window in response to random loss packets. See <http://ieeexplore.ieee.org/xpl/freeabs_all.jsp?arnumber=1177186>
YeAH-TCP is a sender-side high-speed enabled TCP congestion control algorithm, which uses a mixed loss/delay approach to compute the congestion window. It's design goals target high efficiency, internal, RTT and Reno fairness, resilience to link loss while keeping network elements load as low as possible. For further details look here: http://wil.cs.caltech.edu/pfldnet2007/paper/YeAH_TCP.pdf
TCP-Illinois is a sender-side modification of TCP Reno for high speed long delay links. It uses round-trip-time to adjust the alpha and beta parameters to achieve a higher average throughput and maintain fairness. For further details see: http://www.ews.uiuc.edu/~shaoliu/tcpillinois/index.html
Select the TCP congestion control that will be used by default for all connections. config DEFAULT_BIC bool "Bic" if TCP_CONG_BIC=y config DEFAULT_CUBIC bool "Cubic" if TCP_CONG_CUBIC=y config DEFAULT_HTCP bool "Htcp" if TCP_CONG_HTCP=y config DEFAULT_HYBLA bool "Hybla" if TCP_CONG_HYBLA=y config DEFAULT_VEGAS bool "Vegas" if TCP_CONG_VEGAS=y config DEFAULT_VENO bool "Veno" if TCP_CONG_VENO=y config DEFAULT_WESTWOOD bool "Westwood" if TCP_CONG_WESTWOOD=y config DEFAULT_RENO bool "Reno"
RFC2385 specifies a method of giving MD5 protection to TCP sessions. Its main (only?) use is to protect BGP sessions between core routers on the Internet. If unsure, say N.