Re: [lwip-devel] Adding a static route table in LwIP

[pradip de]

Thanks Ivan. I will then create conditionally compiled public accessor methods for the destination cache and submit a patch shortly.

best,

Pradip

On Sat, May 30, 2015 at 10:33 AM, Ivan Delamer <address@hidden> wrote:

Hi Pradip,

The truth is, there isn't just one way to do it right.

For example, in the ND6 module, we follow RFC closely and have separate next-hop and destination tables.

Many stacks implement both in a single table.

Static entries are sometimes implemented in the same tables as well, not a separate module. It can be done in a split table or single table approach.

Maybe exposing static methods is not the best idea, instead you can add some public access methods that are conditionally compiled. That's what I would do, and it is then easy to submit as a patch.

Once you have a patch ready, post it in Savannah and advertise it in the users list.

Cheers
Ivan

Date: Fri, 29 May 2015 10:23:36 -0700
From: pradip de <address@hidden>
To: lwip-devel <address@hidden>
Subject: Re: [lwip-devel] Adding a static route table in LwIP
Message-ID:
        <CACwO0gtv0Z9Sn=address@hidden>
Content-Type: text/plain; charset="utf-8"

Hi Ivan,

>From what it appears to me, if I have to add the nexthop gateway lookup

code outside of nd6.c and in ethip6_output() as you suggested, then I could
do something like this in ethip6_output() :-
==================================================================================
*+#if LWIP_IPV6_STATIC_ROUTES_SUPPORT*
*+  /* See if a gateway is present for the destination address in the
static route table */*
*+  gateway = ip6_get_gateway(netif, ip6addr);*
*+  if (gateway != NULL) {*
*+    i = nd6_find_destination_cache_entry(ip6addr);*
*+    if (i < 0) {*
*+      /* Not found. Create a new destination entry. */*
*+      i = nd6_new_destination_cache_entry();*
*+      if (i < 0) {*
*+        /* Could not create a destination cache entry. */*
*+        return ERR_MEM;*
*+      }*
*+    }*
*+*
*+    /* Add gateway as next hop into destination cache */*
*+    destination_cache[i].pmtu = netif->mtu; /* Start with netif mtu,
correct through ICMPv6 if necessary */*
*+    ip6_addr_copy(destination_cache[i].next_hop_addr, gateway);*
*+  }*
*+#endif*
*   /* Get next hop record. */*
*   i = nd6_get_next_hop_entry(ip6addr, netif);*
*   if (i < 0) {*
==================================================================================

However, that would require exposing of the two static nd6 functions to
find/insert entries into the destination cache. This is one reason why I
was preferring to have the nexthop gateway fetching code integrated into
nd6_get_next_hop_entry(..) although still remaining within STATIC_ROUTE
conditional compilation flags. Please let me know what your thoughts are on
this.

PS: The ip6_get_gateway(..) could be potentially replaced by a suitable
gateway-fetching hook but that is a separate issue.

Thanks,
Pradip

On Thu, May 28, 2015 at 10:02 AM, pradip de <address@hidden> wrote:

Hi Ivan,
Thanks for your input. Your suggestion of keeping the route selection
separate seems doable. I could have my routing functions in a separate
static_route_table.c/h file and enable the LWIP_HOOK_IPV6_ROUTE macro with
the route lookup function.
However, regarding the next-hop selection based on the gateway, I had
added the following snippet in the nd6_get_next_hop_entry(..) for
populating the next_hop within the destination cache's
*nd6_cached_destination_index* entry. After the destination cache's
nexthop entry is populated, the neighbor cache entry is also populated
accordingly. All this happens inside this function in nd6.c.
However, if I have to do this prior to nd6_get_nest_hop_entry(..) in
ethip6_output(), could you suggest how the destination cache's cached index
entries could be populated appropriately?

The modification that I made in nd6_get_next_hop_entry(..) in nd6.c is
something like this:-


*    }*
*      else {*
*#if LWIP_IPV6_ROUTER_SUPPORT*
*        /* We need to select a router. */*
*        i = nd6_select_router(ip6addr, netif);*
*        if (i < 0) {*
*          /* No router found. */*
*
ip6_addr_set_any(&(destination_cache[nd6_cached_destination_index].destination_addr));*
*          return ERR_RTE;*
*        }*
*        destination_cache[nd6_cached_destination_index].pmtu =
netif->mtu; /* Start with netif mtu, correct through ICMPv6 if necessary */*
*
ip6_addr_copy(destination_cache[nd6_cached_destination_index].next_hop_addr,
default_router_list[i].neighbor_entry->next_hop_address);*

*+#if LWIP_IPV6_STATIC_ROUTES_SUPPORT*
*+       /* See if a static route is configured for the destination
address */*
*+      i = ip6_find_route_entry(ip6addr);*
*+       if (i >= 0) {*
*+          if (static_route_table[i].gateway != NULL) {*
*+
ip6_addr_copy(destination_cache[nd6_cached_destination_index].next_hop_addr,
*static_route_table[i].gateway);*
*+           }*
*+        }*
*+#endif*
*#else*
*
ip6_addr_set_any(&(destination_cache[nd6_cached_destination_index].destination_addr));*
*        return ERR_RTE;*
*#endif /* LWIP_IPV6_ROUTER_SUPPORT */*

Thanks,
Pradip

On Wed, May 27, 2015 at 9:45 AM, Ivan Delamer <address@hidden>
wrote:

Date: Tue, 26 May 2015 17:06:48 -0700

From: pradip de <address@hidden>
To: address@hidden
Subject: Re: [lwip-devel] Adding a static route table in LwIP
Message-ID:
        <
address@hidden>
Content-Type: text/plain; charset="utf-8"

Hi Ivan,

Thanks again for the suggestion.

The LWIP_HOOK_IP6_ROUTE seems like a callback to higher level
implementation of a routing function. Sure it could be used for a static
route check as well. However, the purpose of this hook is only to return
an
outgoing netif, correct?

But what if the static route entry has a gateway that needs to be picked
up
during selection of a next hop. There needs to be logic in
nd6_get_next_hop
code that looks up the static route table to fetch the gateway as the
neighbor to send to.

For some reason it seems to me that a static route table is a basic
feature
and could be a separate part(albeit within conditional compilation flags)
of the core IP6 routing mechanism instead of as a plugin or hook. Plugins
or hooks are probably apt for hooking up advanced or sophisticated
routing
functions.

Thanks,

Pradip

Yes, LWIP_HOOK_IP6_ROUTE would check your static route table and return
the suitable netif. Based on netif selection, the stack would select a
suitable source address.

In your netif->output_ip6 function, you resolve the next hop. Take a look
at ethip6_output(), you can use it as a template. You could insert your
static route lookup code before the nd6_get_next_hop_entry() call. You
don't need to use ethip6_output(), you can choose your own implementation
when you add your netif.

Because static routing can be done in so many ways, I believe it should
remain separate from ND6. We aim to be RFC compliant. I don't know that we
could come up with a static route module that would satisfy everyone.

My suggestion is that you post your work on Savannah as a patch, so that
other people can benefit from it. If we see enough interest over time, and
it proves stable, we can look at adding it to the master branch. That's
actually how the IPv6 code started, as an optional patch. We may also
create a development branch for this if we have several developers working
on it.

Cheers
Ivan


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