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#
# IP configuration
#
config IP_MULTICAST
bool "IP: multicasting"
depends on INET
help
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-itg.lbl.gov/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.
config IP_ADVANCED_ROUTER
bool "IP: advanced router"
depends on INET
---help---
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 will also get 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 off use:
echo 0 > /proc/sys/net/ipv4/conf/<device>/rp_filter
or
echo 0 > /proc/sys/net/ipv4/conf/all/rp_filter
If unsure, say N here.
config IP_MULTIPLE_TABLES
bool "IP: policy routing"
depends on IP_ADVANCED_ROUTER
---help---
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, if you also say Y to "Use TOS
value as routing key" below, the TOS (Type-Of-Service) field of the
packet can be used for routing decisions as well. In addition, if
you say Y here and to "Fast network address translation" below,
the router will also be able to modify source and destination
addresses of forwarded packets.
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.inr.ac.ru/ip-routing/>.
If unsure, say N.
config IP_ROUTE_FWMARK
bool "IP: use netfilter MARK value as routing key"
depends on IP_MULTIPLE_TABLES && NETFILTER
help
If you say Y here, you will be able to specify different routes for
packets with different mark values (see iptables(8), MARK target).
config IP_ROUTE_NAT
bool "IP: fast network address translation"
depends on IP_MULTIPLE_TABLES
help
If you say Y here, your router will be able to modify source and
destination addresses of packets that pass through it, in a manner
you specify. General information about Network Address Translation
can be gotten from the document
<http://www.csn.tu-chemnitz.de/~mha/linux-ip-nat/diplom/nat.html>.
config IP_ROUTE_MULTIPATH
bool "IP: equal cost multipath"
depends on IP_ADVANCED_ROUTER
help
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.
config IP_ROUTE_TOS
bool "IP: use TOS value as routing key"
depends on IP_ADVANCED_ROUTER
help
The header of every IP packet carries a TOS (Type Of Service) value
with which the packet requests a certain treatment, e.g. low
latency (for interactive traffic), high throughput, or high
reliability. If you say Y here, you will be able to specify
different routes for packets with different TOS values.
config IP_ROUTE_VERBOSE
bool "IP: verbose route monitoring"
depends on IP_ADVANCED_ROUTER
help
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").
config IP_ROUTE_LARGE_TABLES
bool "IP: large routing tables"
depends on IP_ADVANCED_ROUTER
help
If you have routing zones that grow to more than about 64 entries,
you may want to say Y here to speed up the routing process.
config IP_PNP
bool "IP: kernel level autoconfiguration"
depends on INET
help
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.
config IP_PNP_DHCP
bool "IP: DHCP support"
depends on IP_PNP
---help---
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/nfsroot.txt> for details.
config IP_PNP_BOOTP
bool "IP: BOOTP support"
depends on IP_PNP
---help---
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/nfsroot.txt> for details.
config IP_PNP_RARP
bool "IP: RARP support"
depends on IP_PNP
help
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/nfsroot.txt> for
details.
# not yet ready..
# bool ' IP: ARP support' CONFIG_IP_PNP_ARP
config NET_IPIP
tristate "IP: tunneling"
depends on INET
---help---
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; check out
<http://anchor.cs.binghamton.edu/~mobileip/LJ/index.html>).
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.
config NET_IPGRE
tristate "IP: GRE tunnels over IP"
depends on INET
help
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.
config NET_IPGRE_BROADCAST
bool "IP: broadcast GRE over IP"
depends on IP_MULTICAST && NET_IPGRE
help
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.
config IP_MROUTE
bool "IP: multicast routing"
depends on IP_MULTICAST
help
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.
config IP_PIMSM_V1
bool "IP: PIM-SM version 1 support"
depends on IP_MROUTE
help
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.
config IP_PIMSM_V2
bool "IP: PIM-SM version 2 support"
depends on IP_MROUTE
help
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.
config ARPD
bool "IP: ARP daemon support (EXPERIMENTAL)"
depends on INET && EXPERIMENTAL
---help---
Normally, 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. For small networks having a few
hundred directly connected hosts or less, keeping this address
resolution (ARP) cache inside the kernel works well. However,
maintaining an internal ARP cache does not work well for very large
switched networks, and will use a lot of kernel memory if TCP/IP
connections are made to many machines on the network.
If you say Y here, the kernel's internal ARP cache will never grow
to more than 256 entries (the oldest entries are expired in a LIFO
manner) and communication will be attempted with the user space ARP
daemon arpd. Arpd then answers the address resolution request either
from its own cache or by asking the net.
This code is experimental and also obsolete. If you want to use it,
you need to find a version of the daemon arpd on the net somewhere,
and you should also say Y to "Kernel/User network link driver",
below. If unsure, say N.
config INET_ECN
bool "IP: TCP Explicit Congestion Notification support"
depends on INET
---help---
Explicit Congestion Notification (ECN) allows routers to notify
clients about network congestion, resulting in fewer dropped packets
and increased network performance. This option adds ECN support to
the Linux kernel, as well as a sysctl (/proc/sys/net/ipv4/tcp_ecn)
which allows ECN support to be disabled at runtime.
Note that, on the Internet, there are many broken firewalls which
refuse connections from ECN-enabled machines, and it may be a while
before these firewalls are fixed. Until then, to access a site
behind such a firewall (some of which are major sites, at the time
of this writing) you will have to disable this option, either by
saying N now or by using the sysctl.
If in doubt, say N.
config SYN_COOKIES
bool "IP: TCP syncookie support (disabled per default)"
depends on INET
---help---
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, note that SYN cookies aren't enabled by default;
you can enable them by saying Y to "/proc file system support" and
"Sysctl support" below and executing the command
echo 1 >/proc/sys/net/ipv4/tcp_syncookies
at boot time after the /proc file system has been mounted.
If unsure, say N.
source "net/ipv4/netfilter/Kconfig"