% % $XORP: xorp/docs/user_manual/interfaces.tex,v 1.11 2006/08/02 05:31:48 pavlin Exp $ % \chapter{Network Interfaces} \label{interfaces} \section{Network Interfaces Terminology and Concepts} A router receives packets via its network interfaces from its neighboring routers. Some of those packets will be destined for the router itself, but most of then will normally be forwarded on via another network interface to another router or to locally connected hosts. There are many different types of network interface, such as Ethernet, ATM, DS3, or ISDN. Sometimes the underlying physical interface will need explicit configuration before it can establish a link, and sometimes the link requires no configuration. In addition, some network interfaces behave from a routing point of view as if they were really multiple interfaces, in that the router may have to forward packets between different ``channels'' on the same interface. We choose to distinguish in a XORP router between physical interfaces (which we call {\it interfaces}, and logical interfaces, which we call virtual interfaces or {\it vifs}. An example of a {\it interface} might be an Ethernet card. An example of a {\it vif} might be one of many VLANs configured on that Ethernet\footnote{Currently (August 2006), VLANs are not supported in XORP.}. Conceptually, XORP routes packets between vifs. Thus it is also vifs that are given IP addresses. Each interface may contain many vifs. Conversely every vif is always part of an interface, although some interfaces such as the loopback interface do not have a physical realisation. The XORP naming convention for vifs is that they are named as they would be in the underlying forwarding path. For example, if the forwarding path is implemented in the FreeBSD kernel, then {\stt fxp0} might denote a 100-base-T Ethernet vif (with no VLAN). On a router using Linux as the forwarding path, the same vif might be called {\stt eth0}. If a physical interface cannot support multiple vifs, or if there's a default vif on a physical interface, then the interface name and the vif name will normally be the same. Again, this is determined by the underlying forwarding path. A common example would be Ethernet without VLANs, where the interface and vif might both be named {\stt fxp0} on FreeBSD or both called {\stt eth0} on Linux. \newpage \section{Configuring Network Interfaces} A XORP router will only use interfaces that it has been explicitly configured to use. For protocols such as RIP that are explicitly aware of interfaces, only configured interfaces will be used. Even for protocols such as BGP that don't directly associate peerings with interfaces, if the next-hop router for a routing entry is not through a configured interface, the route will not be installed. \subsection{Configuration Syntax} The available configuration syntax for network interfaces and addresses is as follows: \vspace{0.1in} \noindent\framebox[\textwidth][l]{\scriptsize \begin{minipage}{6in} \begin{alltt} \begin{tabbing} xx\=xx\=xx\=xx\=xx\=\kill interfaces \{\\ \>restore-original-config-on-shutdown: {\it bool}\\ \>interface {\it text} \{\\ \>\>description: {\it text}\\ \>\>mac: {\it macaddr}\\ \>\>mtu: {\it uint}\\ \>\>default-system-config\\ \>\>disable: {\it bool}\\ \>\>vif {\it text} \{\\ \>\>\>disable: {\it bool}\\ \>\>\>address {\it IPv4-addr} \{\\ \>\>\>\>prefix-length: {\it int(1..32)}\\ \>\>\>\>broadcast: {\it IPv4-addr}\\ \>\>\>\>destination: {\it IPv4-addr}\\ \>\>\>\>disable: {\it bool}\\ \>\>\>\}\\ \>\>\>address {\it IPv6-addr} \{\\ \>\>\>\>prefix-length: {\it int(1..128)}\\ \>\>\>\>destination: {\it IPv6-addr}\\ \>\>\>\>disable: {\it bool}\\ \>\>\>\}\\ \>\>\}\\ \>\}\\ \} \end{tabbing} \end{alltt} \end{minipage} } \begin{description} \item{\tt interfaces}: this delimits all the interface configuration information within the XORP configuration file. \item{\tt restore-original-config-on-shutdown}: this flag enables the restoring of the original network configuration when the FEA is shutdown. If it is set to true, then the restoring is enabled, otherwise is disabled. The default is {\stt false} (\ie don't restore the original network configuration). \item{\tt interface}: this delimits the configuration for a particular interface. The parameter is the name of the interface, which must correspond to an interface known to the router forwarding path. For each interface, the following configuration is possible: \begin{description} \item{\tt description}: this is a human-readable description for the interface. It is primarily used to help the router operator remember which interface serves which purpose. It is optional. \item{\tt mac}: This allows the MAC address for the interface to be set. MAC addresses on devices such as Ethernets are usually fixed, but in some cases it is possible to override the built-in default MAC address. The format should be in a form appropriate for the interface type. For an Ethernet interface, this would be six colon-separated 8-bit numbers in hexadecimal, such as {\stt 00:0a:59:9a:f2:ba}. \item{\tt mtu}: This allows the maximum transfer unit (MTU) to be set for the interface as a whole (applying to all VIFs). The value is an integer number of bytes, and should be less than or equal to the largest MTU supported by the physical device. When forwarding, IPv4 packets larger than the MTU will be fragmented unless they the DF bit set, in which case they will be dropped and an ICMP Packet-too-big message will be returned to the sender. \item{\tt default-system-config}: Normally all the interfaces, vifs, and addresses on a XORP router will be configured through the XORP configuration file and command line interface. However, under certain circumstances it is useful to be able to run XORP as a routing daemon without changing the current configuration of interfaces and addresses. This primitive tells XORP to obtain its configuration for this interface by reading the existing configuration back from the forwarding engine rather than by configuring the forwarding engine. If {\tt default-system-config} is used, then the {\tt vif} and {\tt address} sections must not be configured. \item{\tt disable}: this flag disables or enables the interface for routing and forwarding~\footnote{Note that prior to XORP Release-1.1, the {\tt enable} flag was used instead of {\tt disable}.}. It takes the value {\stt true} or {\stt false}. Configuring an interface to be disabled has the same effect as removing its configuration, but without losing what the configuration used to be. \item{\tt vif}: this configures a vif on the corresponding interface. In some cases this may cause the vif to be created; an example might be an Ethernet VLAN. In other cases this merely denotes the start of the configuration for the vif. The parameter is the name of the vif, as understood by the router forwarding engine. For each vif, the following configuration is possible: \begin{description} \item{\tt disable}: this flag disables or enables the vif for routing and forwarding~\footnote{Note that prior to XORP Release-1.1, the {\tt enable} flag was used instead of {\tt disable}.}. It takes the value {\stt true} or {\stt false}. Configuring a vif to be disabled has the same effect as removing its configuration, but without losing what the configuration used to be. \item{\tt address}: this specifies a new IP address for this vif. A single vif might have multiple IP addresses, and might have both IPv4 address and IPv6 addresses. The parameter is either an IPv4 or IPv6 address. For each address, the following configuration is possible: \begin{description} \item{\tt prefix-length}: this gives the prefix length of the subnet connected to this interface. For an IPv4 address, prefix-length must be between 4 and 32. For an IPv6 address, prefix-length must be between 8 and 128. This field is mandatory for each address. \item{\tt broadcast}: this gives the subnet broadcast address for the subnet corresponding to the vif address. It is only needed for IPv4 addresses (it is mandatory), and is needed for historical reasons. It takes the form of an IPv4 address. Normally the broadcast address will have the local hosts part of the subnet address set to all ones. For example, with address 10.0.0.0 and prefix-length 20, the broadcast address will have the last 12 bits set to one, and hence will be 10.0.15.255. \item{\tt destination}: this specifies the destination IP address. It is only relevant for point-to-point interfaces, where the IP addresses at each end of the link need not share an IP subnet. \item{\tt disable}: this flag disables or enables this IP address on this vif~\footnote{Note that prior to XORP Release-1.1, the {\tt enable} flag was used instead of {\tt disable}.}. It takes the value {\stt true} or {\stt false}. Configuring an IP address to be disabled has the same effect as removing its configuration, but without losing what the configuration used to be. \end{description} \end{description} \end{description} \end{description} \newpage \subsection{Example Configurations} We recommend that you select the interfaces that you want to use on your system and configure them as below. Interfaces that you do not wish XORP to use for forwarding should be omitted from the configuration. \subsubsection{Configuring Interface Addresses} \vspace{0.1in} \noindent\framebox[\textwidth][l]{\scriptsize \begin{minipage}{6in} \begin{alltt} \begin{tabbing} xx\=xx\=xx\=xx\=xx\=\kill interfaces \{\\ \>interface dc0 \{\\ \>\>description: "ethernet interface"\\ \>\>disable: false\\ \>\>vif dc0 \{\\ \>\>\>disable: false\\ \>\>\>address 10.10.10.10 \{\\ \>\>\>\>prefix-length: 24\\ \>\>\>\>broadcast: 10.10.10.255\\ \>\>\>\>disable: false\\ \>\>\>\}\\ \>\>\>\\ \>\>\>address 10:10:10:10:10:10:10:10 \{\\ \>\>\>\>prefix-length: 64\\ \>\>\>\>disable: false\\ \>\>\>\}\\ \>\>\>\\ \>\>\}\\ \>\}\\ \} \end{tabbing} \end{alltt} \end{minipage} } \vspace{0.1in} In the example above, the router has only one interface configured. This interface is called {\stt dc0}, and the vif is also called {\stt dc0}. In this case, this is because this interface is an Ethernet inferface, and VLANs are not being used, so the vif is simply the default vif for this interface. The vif has both an IPv4 and an IPv6 address configured. The IPv4 address is {\stt 10.10.10.10}, and connects to the subnet {\stt 10.10.10.0/24} as determined by the prefix-length. Consistent with this, the subnet broadcast address is {\stt 10.10.10.255}. The IPv6 address has a prefix-length of 64 bits, and does not need (or allow) the broadcast address to be explicitly specified. In this case, the internface is not a point-to-point interface, so no destination address is specified. \subsubsection{Using Pre-Configured Interface Addresses} If the {\tt default-system-config} statement is used, as shown in the example belore, it instructs the FEA that the interface should be configured by using the existing interface information from the underlying system. In that case, the {\tt vif} and {\tt address} sections must not be configured. \vspace{0.1in} \noindent\framebox[\textwidth][l]{\scriptsize \begin{minipage}{6in} \begin{alltt} \begin{tabbing} xx\=xx\=xx\=xx\=xx\=\kill interfaces \{\\ \>interface dc0 \{\\ \>\>description: "data interface"\\ \>\>disable: false\\ \>\>default-system-config\\ \>\}\\ \} \end{tabbing} \end{alltt} \end{minipage} } \vspace{0.1in} \newpage \section{Monitoring Network Interfaces} The state of a XORP router's interfaces can be displayed from operational mode using the {\stt show interfaces} command. By itself, {\stt show interfaces} will list information about all the interfaces in the router: \vspace{0.1in} \noindent\framebox[\textwidth][l]{\scriptsize \begin{minipage}{6in} \begin{alltt} \begin{tabbing} xxxxxxxx\=xxxxxxxxxxxxxxxx\=\kill user@hostname> \textbf{show interfaces}\\ dc0/dc0: Flags: mtu 1500\\ \>inet 172.16.0.1 subnet 172.16.0.0/24 broadcast 172.16.0.255\\ \>physical index 1\\ \>ether 00:80:c8:b9:61:09\\ dc1/dc1: Flags: mtu 1500\\ \>inet 172.16.1.1 subnet 172.16.1.0/24 broadcast 172.16.0.255\\ \>physical index 2\\ \>ether 00:80:c8:b9:61:0a\\ dc2/dc2: Flags: mtu 1500\\ \>inet 172.16.2.1 subnet 172.16.2.0/24 broadcast 172.16.0.255\\ \>physical index 3\\ \>ether 00:80:c8:b9:61:0b\\ dc3/dc3: Flags: mtu 1500\\ \>inet 172.16.3.1 subnet 172.16.3.0/24 broadcast 172.16.0.255\\ \>physical index 4\\ \>ether 00:80:c8:b9:61:0c\\ fxp0/fxp0: Flags: mtu 1500\\ \>inet 192.150.187.112 subnet 192.150.187.0/25 broadcast 192.150.187.255\\ \>physical index 5\\ \>ether 00:02:b3:10:b4:6c \end{tabbing} \end{alltt} \end{minipage} } \vspace{0.1in} In this case, the router has five Ethernet interfaces, each of which has a single vif. The naming format is {\it interface/vif}. For example {\stt dc1/vlan2} would be vif vlan2 on interface dc1. In the above example, all the vif names are the same as the Ethernet interface names because no VLANs are being used. \vspace{0.1in} To display information about a specific interface, use the {\stt show interfaces $<${\it interface}$>$} command: \vspace{0.1in} \noindent\framebox[\textwidth][l]{\scriptsize \begin{minipage}{6in} \begin{alltt} \begin{tabbing} xxxxxxxx\=xxxxxxxxxxxxxxxx\=\kill user@hostname> \textbf{show interfaces dc1}\\ dc1/dc1: Flags: mtu 1500\\ \>inet 172.16.1.1 subnet 172.16.1.0/24 broadcast 172.16.0.255\\ \>physical index 2\\ \>ether 00:80:c8:b9:61:0a\\ \end{tabbing} \end{alltt} \end{minipage} }