  We consider the generalized Korteweg-de Vries equation $\partial_t u =
-\partial_x(\partial_x^2 u + f(u))$, where $f(u)$ is an odd function of class
$C^3$. Under some assumptions on $f$, this equation admits \emph{solitary
waves}, that is solutions of the form $u(t, x) = Q_v(x - vt - x_0)$, for $v$ in
some range $(0, v_*)$. We study pure two-solitons in the case of the same limit
speed, in other words global solutions $u(t)$ such that \begin{equation}
\label{eq:abstract} \tag{$\ast$} \lim_{t\to\infty}\|u(t) - (Q_v(\cdot - x_1(t))
\pm Q_v(\cdot - x_2(t)))\|_{H^1} = 0, \qquad \text{with}\quad\lim_{t \to
\infty}x_2(t) - x_1(t) = \infty. \end{equation} Existence of such solutions is
known for $f(u) = |u|^{p-1}u$ with $p \in \mathbb{Z} \setminus \{5\}$ and $p >
2$. We describe the~dynamical behavior of any solution satisfying
\eqref{eq:abstract} under the assumption that $Q_v$ is linearly unstable (which
corresponds to $p > 5$ for power nonlinearities). We prove that in this case
the sign in \eqref{eq:abstract} is necessarily "$+$", which corresponds to an
attractive interaction. We also prove that the~distance $x_2(t) - x_1(t)$
between the solitons equals $\frac{2}{\sqrt v}\log(\kappa t) + o(1)$ for some
$\kappa = \kappa(v) > 0$.
