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nic_router: support domain-local ARP

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Improve ARP handling code in general:
Make the several cases and their handling more clear by using a more
readable if/else statement structure. Drop gratuitous ARP requests.

Domain-local ARP:
Handle ARP packets that target local IPs other than the routers IP
(forward them to all other interfaces of the domain).

Issue
This commit is contained in:
Martin Stein 2017-11-13 12:45:13 +01:00 committed by Christian Helmuth
parent bfddad17a3
commit 0a77987778
2 changed files with 76 additions and 26 deletions
repos/os/src/server/nic_router
interface.ccinterface.h

92
repos/os/src/server/nic_router/interface.cc

@ -548,6 +548,12 @@ void Interface::_handle_dhcp_request(Ethernet_frame &eth,
}
void Interface::_domain_broadcast(Ethernet_frame &eth, size_t eth_size)
{
throw Drop_packet_warn("domain broadcasts not yet supported");
}
void Interface::_handle_ip(Ethernet_frame &eth,
Genode::size_t const eth_size,
Packet_descriptor const &pkt)
@ -693,20 +699,23 @@ void Interface::_broadcast_arp_request(Ipv4_address const &ip)
}
void Interface::_handle_arp_reply(Arp_packet &arp)
void Interface::_handle_arp_reply(Ethernet_frame &eth,
size_t const eth_size,
Arp_packet &arp)
{
/* do nothing if ARP info already exists */
try {
/* check wether a matching ARP cache entry already exists */
_arp_cache.find_by_ip(arp.src_ip());
if (_config().verbose()) {
log("ARP entry already exists"); }
return;
}
/* create cache entry and continue handling of matching packets */
catch (Arp_cache::No_match) {
/* by now, no matching ARP cache entry exists, so create one */
Ipv4_address const ip = arp.src_ip();
_arp_cache.new_entry(ip, arp.src_mac());
/* continue handling of packets that waited for the entry */
for (Arp_waiter_list_element *waiter_le = _foreign_arp_waiters.first();
waiter_le; )
{
@ -717,6 +726,15 @@ void Interface::_handle_arp_reply(Arp_packet &arp)
destroy(waiter.src()._alloc, &waiter);
}
}
if (_ip_config().interface.prefix_matches(arp.dst_ip()) &&
arp.dst_ip() != _router_ip())
{
/*
* Packet targets IP local to the domain's subnet and doesn't target
* the router. Thus, forward it to all other interfaces of the domain.
*/
_domain_broadcast(eth, eth_size);
}
}
@ -726,26 +744,10 @@ Ipv4_address const &Interface::_router_ip() const
}
void Interface::_handle_arp_request(Ethernet_frame &eth,
size_t const eth_size,
Arp_packet &arp)
void Interface::_send_arp_reply(Ethernet_frame &eth,
size_t const eth_size,
Arp_packet &arp)
{
/*
* We handle ARP only if it asks for the routers IP or if the router
* shall forward an ARP to a foreign address as gateway. The second
* is the case if no gateway attribute is specified (so we're the
* gateway) and the address is not of the same subnet like the interface
* attribute.
*/
if (arp.dst_ip() != _router_ip() &&
(_ip_config().gateway_valid ||
_ip_config().interface.prefix_matches(arp.dst_ip())))
{
if (_config().verbose()) {
log("Ignore ARP request"); }
return;
}
/* interchange source and destination MAC and IP addresses */
Ipv4_address dst_ip = arp.dst_ip();
arp.dst_ip(arp.src_ip());
@ -761,6 +763,46 @@ void Interface::_handle_arp_request(Ethernet_frame &eth,
}
void Interface::_handle_arp_request(Ethernet_frame &eth,
size_t const eth_size,
Arp_packet &arp)
{
if (_ip_config().interface.prefix_matches(arp.dst_ip())) {
/* ARP request for an IP local to the domain's subnet */
if (arp.src_ip() == arp.dst_ip()) {
/* gratuitous ARP requests are not really necessary */
throw Drop_packet_inform("gratuitous ARP request");
} else if (arp.dst_ip() == _router_ip()) {
/* ARP request for the routers IP at this domain */
_send_arp_reply(eth, eth_size, arp);
} else {
/* forward request to all other interfaces of the domain */
_domain_broadcast(eth, eth_size);
}
} else {
/* ARP request for an IP foreign to the domain's subnet */
if (_ip_config().gateway_valid) {
/* leave request up to the gateway of the domain */
throw Drop_packet_inform("leave ARP request up to gateway");
} else {
/* try to act as gateway for the domain as none is configured */
_send_arp_reply(eth, eth_size, arp);
}
}
}
void Interface::_handle_arp(Ethernet_frame &eth, size_t const eth_size)
{
/* ignore ARP regarding protocols other than IPv4 via ethernet */
@ -770,7 +812,7 @@ void Interface::_handle_arp(Ethernet_frame &eth, size_t const eth_size)
error("ARP for unknown protocol"); }
switch (arp.opcode()) {
case Arp_packet::REPLY: _handle_arp_reply(arp); break;
case Arp_packet::REPLY: _handle_arp_reply(eth, eth_size, arp); break;
case Arp_packet::REQUEST: _handle_arp_request(eth, eth_size, arp); break;
default: error("unknown ARP operation"); }
}

10
repos/os/src/server/nic_router/interface.h

@ -102,12 +102,18 @@ class Net::Interface
void _handle_arp(Ethernet_frame &eth, Genode::size_t const eth_size);
void _handle_arp_reply(Arp_packet &arp);
void _handle_arp_reply(Ethernet_frame &eth,
Genode::size_t const eth_size,
Arp_packet &arp);
void _handle_arp_request(Ethernet_frame &eth,
Genode::size_t const eth_size,
Arp_packet &arp);
void _send_arp_reply(Ethernet_frame &eth,
Genode::size_t const eth_size,
Arp_packet &arp);
void _handle_dhcp_request(Ethernet_frame &eth,
Genode::size_t eth_size,
Dhcp_packet &dhcp);
@ -133,6 +139,8 @@ class Net::Interface
void _broadcast_arp_request(Ipv4_address const &ip);
void _domain_broadcast(Ethernet_frame &eth, Genode::size_t eth_size);
void _pass_prot(Ethernet_frame &eth,
Genode::size_t const eth_size,
Ipv4_packet &ip,