netdev - Re: [PATCH net-next v2 1/2] mpls: allow TTL propagation to IP packets to be configured

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Date:   Thu, 9 Mar 2017 19:00:41 -0700
From:   David Ahern <dsa@...ulusnetworks.com>
To:     Robert Shearman <rshearma@...cade.com>, davem@...emloft.net
Cc:     netdev@...r.kernel.org,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        roopa <roopa@...ulusnetworks.com>
Subject: Re: [PATCH net-next v2 1/2] mpls: allow TTL propagation to IP packets
 to be configured

On 3/7/17 5:46 PM, Robert Shearman wrote:
> @@ -244,24 +245,33 @@ static bool mpls_egress(struct mpls_route *rt, struct sk_buff *skb,
>  		payload_type = ip_hdr(skb)->version;
>  
>  	switch (payload_type) {
> -	case MPT_IPV4: {
> -		struct iphdr *hdr4 = ip_hdr(skb);
> +	case MPT_IPV4:
> +		if (rt->rt_ttl_propagate == MPLS_TTL_PROP_ENABLED ||
> +		    (rt->rt_ttl_propagate == MPLS_TTL_PROP_DEFAULT &&
> +		     net->mpls.ip_ttl_propagate)) {
> +			struct iphdr *hdr4 = ip_hdr(skb);
> +
> +			csum_replace2(&hdr4->check,
> +				      htons(hdr4->ttl << 8),
> +				      htons(dec.ttl << 8));
> +			hdr4->ttl = dec.ttl;
> +		}
>  		skb->protocol = htons(ETH_P_IP);
> -		csum_replace2(&hdr4->check,
> -			      htons(hdr4->ttl << 8),
> -			      htons(dec.ttl << 8));
> -		hdr4->ttl = dec.ttl;
>  		success = true;
>  		break;
> -	}
> -	case MPT_IPV6: {
> -		struct ipv6hdr *hdr6 = ipv6_hdr(skb);
> +	case MPT_IPV6:
> +		if (rt->rt_ttl_propagate == MPLS_TTL_PROP_ENABLED ||
> +		    (rt->rt_ttl_propagate == MPLS_TTL_PROP_DEFAULT &&
> +		     net->mpls.ip_ttl_propagate)) {
> +			struct ipv6hdr *hdr6 = ipv6_hdr(skb);
> +
> +			hdr6->hop_limit = dec.ttl;
> +		}
>  		skb->protocol = htons(ETH_P_IPV6);
> -		hdr6->hop_limit = dec.ttl;
>  		success = true;
>  		break;
> -	}

What decrements the TTL if it is not propagated from MPLS to IP?